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date: 17 November 2019

The Conduct and Consequences of War

Summary and Keywords

The academic study of warfare has expanded considerably over the past 15 years. Whereas research used to focus almost exclusively on the onset of interstate war, more recent scholarship has shifted the focus from wars between states to civil conflict, and from war onset to questions of how combatants wage and terminate war. Questioned as well are the longer-term consequences of warfare for countries and their populations. Scholarship has also shifted away from country-conflict-year units of analysis to micro-level studies that are attentive to individual-level motives and explanations of spatial variation in wartime behavior by civilians and combatants within a country or armed conflict. Today, research focuses on variations in how states and rebel groups wage war, particularly regarding when and how wars expand, whether combatants comply with the laws of war, when and why conflicts terminate, and whether conflicts end with a clear military victory or with a political settlement through negotiations. Recent research also recognizes that strategic behavior continues into the post-conflict period, with important implications for the stability of the post-conflict peace. Finally, the consequences of warfare are wide-ranging and complex, affecting everything from political stability to public health, often long after the fighting stops.

Keywords: interstate war, civil war, laws of war, civilian victimization, war termination, war severity, post-conflict peace

Introduction

Over the past 15 years, research by social scientists on the conduct and consequences of war has expanded considerably. Previously, scholarly research had been heavily oriented towards the analysis of the causes of interstate war and its onset. Three simultaneous trends, however, have characterized scholarship on war since the early 2000s. First, studies of the dynamics of civil war have proliferated. Second, war is conceptualized as a series of inter-related stages in which the onset, conduct, and termination of wars as well as post-war relations are analyzed theoretically and empirically in a more integrated fashion. Third, studies have shifted away from country-conflict-year units of analysis to micro-level studies that are sensitive to spatial variation in behavior within a country or conflict.

This article reviews and assesses this body of recent scholarship, which has shifted the focus from war onset to questions of how combatants wage war and what are the longer-term consequences of warfare for countries and their populations. Scholarly research examines the conduct and consequences of both interstate and civil wars.

The analysis is organized into three main sections. It begins with research on how states and rebel groups wage war, with particular attention given to questions regarding war expansion, compliance with the laws of war, and war severity. Section two turns to the literature on war duration, termination, and outcomes. Different explanations are discussed, for when and why wars come to an end; then, the question of how war’s end influences the prospects for a stable post-war peace is considered. In section three, recent scholarship is examined on the consequences of war for post-war trends in political stability and public health. The concluding discussion addresses some of the important contributions associated with recent scholarship on the conduct and consequences of war as well as promising directions for future research.

The Waging of Civil and International Wars

What accounts for the nature of the wars we see? This broad question drives a new research tradition in conflict studies that compliments traditional analyses of war onset by shifting the focus to state behavior during war. This research goes beyond understandings of why states fight one another to engaging questions of why states join ongoing wars, when and why they follow the laws of war, and what explains the severity of wars. Taken together, these questions open the black box of wartime behavior.

Intervention and the Expansion of Interstate Wars

Research on war expansion developed as a natural outgrowth of analyses of war onset: scholars studying why states initiate conflict shifted focus to understand why third parties join ongoing wars. The link between alliances and joining behavior has been central to studies of war expansion, spawning a broad research tradition that focuses on alliances and geography, differences among types of alliances, and the characteristics of alliance members. Siverson and Starr (1991), for example, find a strong interaction effect between geography and alliances, in that a warring neighbor who is an ally increases the likelihood of a state joining an existing conflict. Leeds, Long, and Mitchell (2000) also find that the specific content of alliance obligations is critical to understanding when states choose to intervene, and that states uphold the terms of their alliance commitments nearly 75% of the time. Most recently, Vasquez and Rundlett (2016) found that alliances are essentially a necessary condition for war expansion, highlighting the importance of this factor in explaining joining behavior.

Alliance behavior is also an important topic in the study of democratic wartime behavior. While Choi (2004) presents findings suggesting that democracies are particularly likely to align with one another, Reiter and Stam (2002) provide counter-evidence that democracies are willing to align with non-democracies when it serves their strategic interests. Given the tendency to uphold alliance obligations, and empirical evidence showing that war initiators are more successful when their adversary does not receive third-party assistance (Gartner & Siverson, 1996), recent theoretical research suggests that states, understanding joining dynamics, might manipulate war aims to reduce the likelihood of outside intervention (Werner, 2000).

These studies suggest that war expansion should be understood as the consequence of a decision calculus undertaken by potential joiners. While much of the contemporary literature focuses on alliance behavior, this only indirectly gets at the question of who will join ongoing conflicts. A full explanation of war expansion from this perspective would also require that we explain when states form alliances in the first place. Further, the analyses of Gartner and Siverson (1996) and of Werner (2000) suggest that strategic thinking must be the focus of future research on war expansion. Recent research begins to address this issue: DiLorenzo and Rooney (2018) examine how uncertainty over estimates of third party resolve influence war-making decisions of states, finding that rival states are more likely to initiate conflict when domestic power shifts in potential joiner states (i.e., allies) increase uncertainty over the strength of that alliance commitment. Future research should continue to investigate the links between expectations of third-party behavior and initial war initiation decisions, as this research highlights important selection processes that empirical research has not yet fully explored.

Finally, recent research goes further to connect war initiation and expansion by arguing that commitment problems—one of the key bargaining failures leading to war initiation—also helps explain war expansion. Shirkey (2018) finds that wars caused by commitment rather than information problems are more likely to expand, as they are generally fought over greater war aims, are more severe, and last longer. These factors generate risks and rewards for intervention that encourage expansion.

The literature on interstate war expansion has made progress in the last decade with much closer attention to modeling strategic calculations by combatants and potential interveners. The result has been a better understanding of the interrelationship between onset and joining behavior and the realization that the timing and the sequence in which sides intervene is critical to war expansion (Joyce, Ghosn, & Bayer, 2014).

Expansion of Civil Wars

The analog to studies of war expansion in the interstate context has traditionally been the study of intervention in the civil war context. Research in this field treats the decision to intervene in much the same way as the war expansion literature treats the potential joiner’s decision calculus. That is, intervention is the result of a rational, utility-maximizing decision calculus in which potential interveners consider the costs and benefits of intervention as well as the potential for achieving desired outcomes. Understood in these terms, both domestic and international strategic considerations affect the decision to intervene, with the Cold War geopolitical climate much more conducive to countervailing interventions than the post-Cold War era has been (Regan, 2002a), and peacekeeping-oriented interventions most likely in states with ethnic, trade, military, or colonial ties to the intervening state (Rost & Greig, 2011).

Whether states are most likely to intervene in easy or hard cases is a central question. While Aydin (2010) showed that states will delay intervention when previous interventions by other states have failed to influence the conflict, Rost and Grieg (2011) showed that state-based interventions for peacekeeping purposes are most likely in tough cases—long ethnic wars and conflicts that kill and displace large numbers of civilians. Finally, Gent (2008) shows that the likelihood of success may not affect the intervention decision equally for government and opposition-targeted interventions. He finds that both types of intervention are more likely when governments face stronger rebel groups, thus implying that intervention in support of rebel groups occurs when the likelihood of success is highest, but intervention supporting governments is most likely when states face their most intense challenges.

There are two likely sources of the discrepancies in this literature. First, most analyses have focused exclusively on the intervener’s decision calculus, or the supply side, failing to account for variation in the demand for intervention. Second, there is significant inconsistency in the literature’s treatment of the goals of interveners. Some analyses assume that states intervene to end conflicts, while others don’t make this limiting assumption but still fail to distinguish among interventions for different purposes.

Newer research takes important strides to address these issues. First, Salehyan, Skrede Gleditsch, and Cunningham (2011) developed a theory of third party support for insurgent groups that explicitly modeled both supply-side and demand-side factors driving the intervention decision. They found that demand is greatest among weak rebel groups, but supply is greatest for strong groups. Second, research by Cunningham (2010) explicitly measured whether third party states intervene with independent goals, and Stojek and Chacha (2015) theorized that intervention behavior is driven by economic motivations. Trade ties increase the likelihood of intervention on the side of the government.

Finally, Kathman (2010) focused on contiguous state interveners in examining motives for intervention. He developed a measure of conflict infection risk that predicts the likelihood of conflict spreading to each contiguous state. Empirically, he finds that, as the risk of contagion increases, so does the probability of intervention by at-risk neighbors. This research develops a convincing mechanism and empirical test to explain a subset of interventions and provides a clear link from intervention research to recent research on civil conflict contagion. While the contagion literature is too broad to review here, mechanisms posited for civil war expansion across borders range from refugee flows (Salehyan & Gleditsch, 2006), to ethnic kinship ties (Forsberg, 2014), to increased military expenditures in neighboring states (Phillips, 2015).

The literature on intervention into civil wars has grown significantly over the past decade as internationalization of civil conflicts has become common and often results in escalatory dynamics that are of deep concern to analysts and policymakers.

Compliance With the Laws of War

Scholars have recently begun studying the conditions under which compliance with the laws of war is most likely and the mechanisms most important in determining compliance. This research shifts the focus toward understanding state behavior during war and the strategic and normative considerations that influence decision-making processes of states. Two key questions drive scholarship in this tradition; first, does international law constrain state behavior, even when the state is threatened by severe conflict, and second, can observed compliance be attributed to ratification status, or is it instead a result of strategic decision making?

Scholars have yet to provide conclusive answers to these questions; while compliance is observed in many circumstances, most scholars attribute observed restraint to factors other than international law. Legro (1995), for example, found that international agreements had limited impact on Britain and Germany’s use of unrestricted submarine warfare, strategic bombing of civilian targets, and chemical weapons during WWII. In analyses of civilian targeting during interstate war, Downes (2006) and Valentino, Huth, and Croco (2006) also found that international law itself has little impact on a state’s propensity for civilian targeting. Downes argued that civilian targeting occurs most often when states are fighting protracted wars of attrition and desire to save lives on their own side, or when they intend to annex enemy territory with potentially hostile civilians. Valentino et al. (2006) similarly found that the decision to target civilians is driven by strategic considerations and is unconstrained by treaty obligations relating to the laws of war. Finally, Fazal and Greene (2015) found that observed compliance is explained by identity rather than law; violations are much more common in European vs. non-European dyads than in other types of dyads.

While these analyses suggest that international law has little effect on state behavior and that observed compliance is incidental, Price (1997) and Morrow (2014) argued that law does exert some influence on compliance behavior. Price attributed variation in the use of chemical weapons to the terms of international agreements, arguing that complete bans are more effective than partial bans. Morrow (2014), however, demonstrated that law’s impact varies depending upon issue area, regime characteristics, and adversary identity. Of eight issue areas, he found the worst compliance records on civilian targeting and prisoners of war, which perhaps accounts for the largely negative conclusions drawn by Downes (2006) and Valentino et al. (2006). Additionally, Morrow found, unlike Valentino et al., that democratic states are more likely to comply after ratification than before, suggesting that obligations under international law do affect state behavior, at least in democracies. Finally, he demonstrated that compliance increases significantly when an adversary has also ratified a given treaty, arguing this effect is due to reciprocity.

More recent scholarship expands this research, showing that law may affect state behavior through additional mechanisms that previous research had not considered. For example, Kreps and Wallace (2016) and Wallace (2015) found that public support for state policies as diverse as drone strikes and torture of prisoners of war are critically influenced by international law. International condemnation of U.S. policies reduces public support most when such condemnation focuses on legal critiques. This suggests that international law influences state behavior in democracies through its effect on public opinion, not through liberal norms of nonviolence. Additionally, Appel and Prorok (2018) and Jo and Thompson (2014) showed that external constraints influence states’ compliance behavior. Specifically, Appel and Prorok showed that states target fewer civilians in interstate war when they are embedded in alliance and trade networks dominated by third party states who have ratified international treaties prohibiting the abuse of non-combatants during war. Jo and Thompson showed that states are more likely to grant international observers access to detention centers when they are more reliant upon foreign aid. These findings suggest that international law can influence state behavior indirectly, through pressure exerted by international donors and backers.

Scholarship on compliance with the laws of war in interstate wars has made considerable progress over the past decade. We now know much more about the contingent support of democratic state leaders and publics for compliance with the laws of war. This key finding opens up new areas of research on the strategic efforts of political and military leaders to convince publics of their commitment to international law and whether those strategies are likely to be successful.

Civilian Targeting in Civil War

The mistreatment and deliberate targeting of civilian populations is an active area of research by scholars who study civil wars (Hultman, 2007; Humphreys & Weinstein, 2006; Kalyvas, 2006; Valentino et al., 2004; Weinstein, 2007; Wickham-Crowley, 1990). Most research on this topic treats the use of violence against civilians as a strategic choice; that is, combatants target civilians to induce their compliance, signal resolve, weaken an opponent’s support base, or extract resources from the population. In his seminal work on the topic, Kalyvas (2006) demonstrated that combatants resort to the use of indiscriminate violence to coerce civilian populations when they lack the information and control necessary to target defectors selectively. Similarly, Valentino (2005) and Valentino et al. (2004) found that incumbents are more likely to resort to mass killing of civilians when faced with strong insurgent opponents that they are unable to defeat through more conventional tactics.

More recent analyses have built upon these earlier works, adding levels of complexity to the central theories developed previously and examining new forms of violence that previous studies did not. Balcells (2011) brought political considerations back in, finding that direct violence is most likely in areas where pre-conflict political power between state and rebel supporters was at parity, while indirect violence is most likely in locations where the adversary’s pre-war political support was highest. Wood (2010) accounted for the impact of relative strength and adversary strategy, finding that weak rebel groups, lacking the capacity to protect civilian populations, will increase their use of violence in response to state violence, while strong rebel groups display the opposite pattern of behavior. Lyall (2010a) also found conditionalities in the relationship between state behavior and insurgent reactions, demonstrating that government “sweep” operations are much more effective at preventing and delaying insurgent violence when carried out by forces of the same ethnicity as the insurgent group. Finally, Cohen (2016) advanced research by focusing on wartime sexual violence. She found that rape, like other forms of violence, is used strategically in civil war. Specifically, armed groups use rape as a socialization tactic: groups that recruit through abduction engage in rape at higher rates, to generate loyalty and trust between soldiers.

This large body of research provides many insights into the strategic use of violence against civilians during civil war. However, until recently, little research addressed questions of compliance with legal obligations. With the recent formation of the International Criminal Court, however, states and rebel groups are now subject to legal investigation for failure to comply with basic principles of the laws of war.

Emerging research suggests that the International Criminal Court (ICC) and international law more generally do affect the behavior of civil war combatants. For example, Hillebrecht (2016) found that ICC actions during the Libyan civil war reduced the level of mass atrocities committed in the conflict, while Jo and Simmons (2016) found that the ICC reduces civilian targeting by governments and rebel groups that are seeking legitimacy, suggesting international legal institutions can reduce violations of humanitarian law during civil war. These findings should be tempered, however, by recent research suggesting that ICC involvement in civil wars can, under certain conditions, extend ongoing conflicts (Prorok, 2017).

Finally, beyond the ICC, Stanton (2016) and Jo (2015) both demonstrated that international law constrains civil war actors by establishing standards against which domestic and international constituencies judge the behavior of governments and rebel groups. Particularly when rebels are seeking legitimacy, Jo argues, they are more likely to comply with international legal standards in a variety of areas, from protection of civilian populations to child soldiering. This research suggests that even without direct intervention by the ICC, international law can influence the behavior of governments and rebels engaged in civil war.

While recent research has shown that the laws of war can influence civilian targeting in civil wars, the large loss of civilian life in the Syrian civil war highlights how fragile the commitment to international law can be. It points to important future research questions about when threats of various sanctions by the international community against non-compliance are actually credible and which actors can apply effective coercive pressure.

Losses Suffered in Wars

Recent scholarship has taken up the issue of war severity. Empirical research suggests that the tactics and strategies used by states during war, and the political pressures that compel them to adopt those policies, affect the severity of conflict. Biddle (2004), for instance, argued that war-fighting strategies influence the magnitude of losses sustained during war, and found that states employing the modern system of force reduce their exposure to lethal firepower, thus limiting losses. Valentino, Huth, and Croco (2010) examined the reasons behind different strategic choices, arguing that democratic sensitivity to the costs of war pressure democratic leaders to adopt military policies designed to limit fatalities. They found that increasing military capabilities decreases civilian and military fatalities, while reliance on guerrilla or attrition strategies, as well as fighting on or near one’s own territory, increases fatalities. They reported that democracies are significantly more likely to join powerful alliances and less likely to use attrition or guerrilla strategies, or to fight on their own territory.

Speaking to the conventional wisdom that interstate warfare is on the decline, recent research by Fazal (2014) suggests that modern medical advances mean that, while war has become less fatal, it has not necessarily become less severe. This raises questions about common understandings of broad trends in conflict frequency and severity as well as questions about best practices for measuring conflict severity. Future research should grapple with both of these issues.

Civil war studies have recently begun to focus more on conflict severity as an outcome in need of explanation. Many key explanatory factors in early research mirrored those in interstate war research, making comparison possible. For example, like interstate war, civil war scholarship consistently finds that democracies suffer less severe conflicts than nondemocracies (Heger & Salehyan, 2007; Lacina, 2006; Lujala, 2009). Regarding state military strength, research by Lujala (2009) demonstrated that relative equality between government and rebel forces leads to the deadliest conflicts, as rebels with the strength to fight back will likely inflict more losses than those without the ability to sustain heavy engagement with government forces. Finally, recent research by Balcells and Kalyvas (2014) mirrored work on interstate war by focusing on how the military strategies adopted by combatants affect conflict intensity. They found that civil conflicts fought via conventional means tend to be more lethal than irregular or symmetric nonconventional (SNC) wars, as only the former involve direct confrontations with heavy weaponry. While research on conflict severity is still developing, these studies suggest that democracy, military strength, and strategy are consistent predictors of conflict severity, although the mechanisms posited for the effects of these variables sometimes differ between civil and interstate war.

What this research does not provide clear answers on is how battle losses trend throughout the course of conflict, as most factors examined in the above research are static throughout a conflict. As our ability to measure conflict severity at a more micro temporal and spatial level has improved, emerging research is beginning to address these questions. For example, Hultman, Kathman, and Shannon (2014) find that increasing UN troop presence decreases battlefield deaths by increasing the costs of perpetrating violence. Dasgupta Gawande, and Kapur (2017) also found reductions in insurgent violence associated with implementation of development programs, though the pacifying effects of such programs are conditional upon local state capacity. Additional research shows that trends in violence in Islamist insurgencies vary predictably, with violence suppressed due to anticipated social disapproval during important Islamic holidays (Reese, Ruby, & Pape, 2017). Recent research also suggests local variation in cell-phone coverage affects local levels of insurgent violence, as increasing cell-phone communication improves the state’s ability to gather information and monitor insurgent behavior, thereby reducing insurgent violence (Shapiro & Weidmann, 2015). These recent studies represent an important trend in conflict severity research that more carefully examines the dynamics of escalation and de-escalation within given conflicts, both spatially and temporally. We encourage additional research in this vein.

The Duration, Termination, and Outcome of War

What accounts for the duration, termination, and outcomes of interstate and civil wars, and the durability of the peace that follows these conflicts? These questions represent a central focus of contemporary conflict studies, and are closely linked in terms of their explanations. A major innovation in this literature in the past 10 to 15 years has been the extension of the bargaining model of war from its original application in the context of war onset (Blainey, 1973; Fearon, 1995) to its use in the context of war duration, termination, and outcome.

The turn to bargaining models has placed relative military capabilities and battlefield developments at the center of much of the theoretical literature in this area. This focus, however, has spawned a backlash in recent years, as patterns that contradict the implications of bargaining models are detected and theorized. The bargaining approach and its critiques are discussed in the following sections.

Duration of Wars

Understood within the bargaining framework, war duration is closely linked to factors that influence the relative strength of combatants. Theoretical and empirical research suggests that longer wars occur when opponents of relatively equal strength cannot achieve breakthroughs on the battlefield (Bennett & Stam, 1996; Filson & Werner, 2007b; Slantchev, 2004), although this pattern does not hold for wars involving non-state actors where a large asymmetry in power increases war duration (Sullivan, 2008).

Additional research suggests, however, that relative military strength may not be the best predictor of war duration. Bennett and Stam (1996), for example, demonstrated that military strategy has a large impact on war duration, independent of military strength, with attrition and punishment strategies leading to longer wars than maneuver strategies. The type of political objectives sought by a war initiator may also offset the impact of military strength, as war aims that require significant target compliance generally lead to longer wars (Sullivan, 2008). Still others argue that domestic political sensitivity to concessions-making increases conflict duration, while domestic cost sensitivity leads to shorter wars (Filson & Werner, 2007a; Mattes & Morgan, 2004). Thus, democracies are expected to fight shorter wars (Filson & Werner, 2007b), whereas mixed regimes will fight longer wars as they gamble for resurrection in the face of high domestic costs for war losses (Goemans, 2000). Research by Lyall (2010b), however, suggests that this relationship is conditional upon conflict type, as he found no relationship between democracy and war duration in the context of counterinsurgency wars.

Biddle (2004) more directly challenged bargaining models of war duration by comparing the predictive power of models including traditional measures of relative military capabilities to those accounting for combatants’ methods of force employment. Biddle demonstrated that models taking force employment into account generate more accurate predictions of war duration than those assuming an unconditional relationship between military power and war duration. A second important challenge to traditional applications of bargaining models comes from Reiter (2009). He demonstrated that the argument that decisive battlefield outcomes promote quick termination is conditional upon the absence of commitment problems. When compliance fears dominate information asymmetries, battle losses and the expectation of future losses may not be sufficient to end conflict, as belligerents will continue fighting in pursuit of absolute victory to eliminate the threat of the losing state defecting from post-war settlements. Reiter thus demonstrates that commitment problems and information asymmetries have varying effects on war duration, and both must be accounted for in models of conflict duration and termination.

Despite these critiques, more recent research continues to approach the question of war duration from the bargaining perspective. Shirkey (2012), for example, argued that late third-party joiners to interstate conflicts lengthen those disputes by complicating the bargaining process. Joiners add new issues to the war and increase uncertainty about relative power among combatants, thus requiring additional fighting to reveal information and find a bargained solution. Weisiger (2016) similarly focused on information problems, but attempts to unpack the mechanism by focusing on more specific characteristics of battlefield events. Using new data on the timing of battle deaths for specific war participants, Weisiger found that settlement is more likely after more extensive fighting, and that states are more likely to make concessions after their battle results have deteriorated. Finally, recent research has also begun to problematize resolve, considering how variation in actors’ resolve affects their willingness to stay in a fight or cut losses (Kertzer, 2017). This represents a fruitful area for future research, as conceptually and empirically unpacking resolve will shed new light on costs of war and how they relate to war onset, duration, and termination.

Scholars studying the duration of civil wars also commonly apply a rationalist perspective. Factors that increase the costs of sustaining the fight generally shorten wars, while those that raise the costs of making concessions tend to lengthen conflicts. Along these lines, research suggests that the availability of contraband funding for rebel groups lengthens conflicts by providing rebels with the economic resources to sustain their campaigns (Fearon, 2004). However, additional research demonstrates that the influence of contraband is mitigated by fluctuations in its market value (Collier, Hoeffler, & Söderbom, 2004), by how rebels earn funding from resources (through smuggling versus extortion; Conrad, Greene, Igoe Walsh, & Whitaker, 2018), and by the composition of state institutions (Wiegand & Keels, 2018).

Research suggests that structural conditions also affect civil war duration, such as the stakes of war, ethnic divisions, and the number of combatants involved. For example, ethnic conflicts over control of territory are generally longer than those fought over control of the central government (Balch-Lindsay & Enterline, 2000; Collier et al., 2004; Fearon, 2004). Regarding the role of ethnicity, Wucherpfennig, Metternich, Cederman, and Skrede Gleditsch (2012) demonstrated that the effect of ethnic cleavages is conditional on their relationship to political institutions. Regarding the complexity of the conflict, Cunningham (2011) found that civil wars with a greater number of combatants on each side are longer than those with fewer combatants. Findley (2013), however, showed that the number of conflict actors has varying effects across different stages of conflict, encouraging cooperation early on while impeding lasting settlement.

Third party intervention has also received significant attention in the civil war duration literature, with scholars generally arguing that intervention affects duration by augmenting the military strength of combatants. Empirical findings in early studies are mixed, however; while results consistently show that unbiased intervention or simultaneous intervention on both sides of a conflict increase war duration (Balch-Lindsay & Enterline, 2000; Balch-Lindsay, Enterline, & Joyce, 2008; Regan, 2002b), biased interventions generate more inconsistent results.

In a valuable study addressing limitations of earlier research, Cunningham (2010) focused on the goals of third parties, and found that when interveners pursue agendas that are independent of those of the internal combatants, wars are more difficult to terminate due to decreased incentives to negotiate and a higher likelihood that commitment problems stymie settlements. This suggests that the empirical finding that intervention lengthens war may be driven by a subset of cases in which third parties intervene with specific goals. Ultimately, analyses focused on intervention do not account for the potential selection effect that influences when states will intervene. If Gent (2008) is correct, biased intervention should be most likely when the power ratio between government and rebel forces is close to parity, a factor which, if ignored, may bias the results of these analyses.

More recent studies have continued to unpack intervention, demonstrating that there are important distinctions beyond the biased versus balanced debate. Sawyer, Cunningham, and Reed (2015), for example, showed that different types of external support affect rebel fighting capacity differently. Specifically, fungible types of support like financial and arms transfers are particularly likely to lengthen conflict because they increase uncertainty over relative power. Similarly, Narang (2015) also focused on the uncertainty induced by external support. He showed that humanitarian assistance inadvertently increases both actors’ uncertainty over relative power, thereby prolonging civil war.

Until recently, this literature suffered from a major weakness in that it relied empirically on state-level variables that did not fully capture the dyadic nature of its theoretical propositions. Cunningham, Skrede Gleditsch, and Salehyan (2013) new dyadic data represents an important contribution to the field, as it explicitly measures the relative strength, mobilization capacity, and fighting capacity of rebel groups and applies a truly dyadic empirical approach. New research in this field should continue to approach questions of war duration and outcome with dyadic data and theory along with more micro-level studies that seek to explain variation in rebel and state fighting across different geographic locations and over time (e.g., Greig, 2015).

Ending Wars as a Bargaining Process

Interstate wars rarely end in the complete destruction of the defeated party’s military forces. Instead, new information is revealed through combat operations and negotiating behavior which enables belligerents to converge on a mutually agreeable settlement short of total war. Wittman (1979) provided the first formal articulation of the bargaining model in the context of war termination. He argued theoretically that war continues until both adversaries believe they can be made better off through settlement. Subsequent analyses have focused on both the battlefield conditions and strategies of negotiations leading states to believe settlement is the better option.

These analyses show that, as a state’s resources are depleted from battle losses, it has incentives to negotiate a settlement more acceptable to its adversary rather than suffer total defeat (Filson & Werner, 2002; Smith & Stam, 2004). Further, fighting battles reduces uncertainty by revealing information about resolve, military effectiveness, and the true balance of power between adversaries, causing expectations on the likely outcome of the war to converge, and making settlement possible (Wagner, 2000). Wartime negotiations provide adversaries with additional information, which Slantchev (2011) argued makes war termination more likely.

Challenging traditional notions regarding the likelihood of termination in the face of large asymmetries in capabilities, Slantchev (2011) argued that war termination depends upon states’ abilities to both impose and bear the costs of fighting. If a weaker state can minimize the costs it bears while forcing its adversary to expand its war effort, the benefits of fighting relative to its costs are reduced, and the stronger state may choose termination. The implication of this argument relates closely to Biddle’s (2004) empirical critique of the bargaining literature, which finds modern methods of force employment can mitigate losses during war, thereby shifting the balance of costs and benefits independent of relative military capabilities. Reiter’s (2009) critique of bargaining approaches also has implications for war termination. While traditional approaches argue that fighting battles reveals information and increases the likelihood of termination, Reiter suggested that this is only the case if belligerents expect their opponent to comply with the post-war status quo. If commitment problems are severe, information revealed during battles and war-time negotiations will have little effect on termination.

Biddle’s argument that country-year measures of military capabilities are inexact and crude proxies for the concepts advanced in theoretical models is a strong one that should be taken seriously by scholars. We therefore appreciate the contributions of Ramsay (2008) and Weisiger (2016), which use more fine-grained battle trend data rather than country-level measures of military capabilities to empirically test the implications of bargaining theories of war termination, and advocate future research adopting this strategy for testing the implications of bargaining theories.

Much of the literature on civil war termination also focuses on how battlefield developments affect the termination of civil wars. Collier et al. (2004) built on the idea of war as an information revelation mechanism, arguing that the probability of settlement should increase as war duration increases and more information is revealed regarding the relative strength of each side. Others focus on the costs of battle, with research showing that settlements are more likely when the costs of battle are high and the relative payoffs from victory decrease (Walter, 2002). Also, a relatively equal balance of power between combatants creates a mutually hurting stalemate, in which neither side can achieve victory, and settlement becomes more likely (Walter, 2002).

Empirical results support many of these theoretical predictions. Several scholars show that the longer a civil war lasts, the more likely it is to terminate (Collier et al., 2004; Fearon,, 2004; Regan, 2002b), and that the probability of negotiated settlement increases as conflict duration increases (Mason, Weingarten, & Fett, 1999). The magnitude of conflict, measured as total war deaths, also correlates positively with the probability of adversaries initiating negotiations (Walter, 2002). Finally, Walter (2002) found that military stalemates significantly increase the likelihood of negotiations as well as the implementation of a ceasefire.

While these results support the theoretical predictions surrounding “hurting stalemates,” Walter’s coding of stalemates does not account for the timing of the stalemate or the number of stalemates that occur throughout the course of conflict. We therefore see great value in more recent research that uses new micro-level data to more closely capture actual battle dynamics and incorporate more information at the conflict and group-level. For example, Hultquist (2013) used a novel troop strength measure to better capture relative strength between rebel and government forces. He found that relative power parity increases the likelihood of negotiated settlement, while power imbalances extend civil war. Making use of fine-grained data on battle event dates and locations, Greig (2015) showed that the location, and changes in location over time, of battle events relays information to combatants that, in turn, affects their willingness to negotiate and settle their conflicts. We encourage additional research in this vein moving forward.

Domestic-Level Factors and War Termination

Recent research suggests that domestic political conditions influence war termination. Specifically, domestic political accountability, the domestic audience’s expectations, and cost-sensitivity affect leaders’ decisions to continue fighting versus settling on specific terms (Mattes & Morgan, 2004). Along these lines, Goemans (2000) argued that the postwar fate of leaders influences their choice between terminating and continuing a war. The threat of severe punishment by domestic actors increases the costs of war losses for leaders of semi-repressive regimes, leading them to continue fighting a war they are losing in the hope of achieving victory. Thus, war termination does not follow strictly from battle trends.

Empirically, Goemans (2000) found that losing mixed regimes suffer significantly more battle deaths than democratic or autocratic losers, and that wars fought against losing mixed regimes last, on average, almost twice as long as those fought against either democratic or autocratic losers. Taken together, these results suggest that mixed regime leaders are likely to sustain rather than terminate a losing war, and more generally, that regime type significantly influences war termination. Croco (2015) refined Goemans’s work by arguing that the individual responsibility of leaders for involving their country in a war has important effects on war termination patterns, with culpable leaders more likely to fight for victory in order to avoid being punished domestically for poor wartime performance. Croco and Weeks (2013) refined this logic further, showing that only culpable leaders from democracies and vulnerable nondemocracies face increased punishment risk from war losses. Koch and Sullivan (2010) provide another take on the relationship between domestic politics and war termination, demonstrating that partisanship significantly affects democratic states’ war termination decisions. Faced with declining approval for military interventions, their results demonstrate, right-leaning governments will continue the fight, while left-leaning executives will be more likely to end their military engagements.

The analog to studying domestic-level factors in interstate conflict would be to examine the effect of internal state and rebel characteristics on civil war termination. Traditionally, civil war studies have focused only on state characteristics, as data on rebel groups’ organization and internal characteristics has been unavailable. Early research argued that state capacity, regime characteristics, and ethnic/religious divisions influenced war termination by influencing the balance of power, accountability of leaders, and stakes of conflict, but empirical results provided mixed support for these theories (e.g., DeRouen & Sobek, 2004; Svensson, 2007; Walter, 2002).

More recent research has made significant strides in understanding how internal characteristics of combatants affect civil conflict termination by using new data to explore how the composition and practices (i.e., leader characteristics, governance, and internal cohesion) of rebel groups influence civil conflict dynamics. This research demonstrates that some of the same leader-accountability mechanisms that affect interstate war termination also influence civil conflict. For example, Prorok (2016) used novel data on rebel group leaders to show that culpable leaders are less willing to terminate or settle for compromise outcomes than their non-culpable counterparts in civil wars, just like in interstate conflicts. Heger and Jung (2017) also advanced existing research by using novel data on rebel service provision to civilian populations to explore how good rebel governance affects conflict negotiations. They found that service-providing rebels are more likely to engage in negotiations and to achieve favorable results, arguing that this reflects the lower risk of spoilers from groups with broad support and centralized power structures. Finally, Findley and Rudloff (2012) examined rebel group fragmentation’s effects on conflict termination and outcomes. Using computational modeling, they find that fragmentation only sometimes increases war duration (on fragmentation, also see Cunningham, 2014).

These studies underscore the value of exploring rebel group internal structures and practices in greater detail in future research, as they have an important impact on how, and when, civil wars end.

Victory/Defeat in Wars

Recent scholarship on victory and defeat in war suggests, as in the duration and termination literatures, that domestic politics, strategies of force employment, military mechanization, and war aims mediate the basic relationship between military strength and victory. Empirical results show that strategy choices and methods of force employment have a greater impact on war outcomes than relative military capabilities (Biddle, 2004; Stam, 1996), that high levels of mechanization within state militaries actually increase the probability of state defeat in counterinsurgency wars (Lyall & Wilson, 2009), and that weak states win more often when they employ an opposite-strategy approach in asymmetric conflicts (Arreguin-Toft, 2006) or when the stronger party’s war aims require high levels of target compliance (Sullivan, 2007). High relative losses and increasing war duration also decrease the likelihood of victory for war initiators, even if prewar capabilities favored the aggressor (Slantchev, 2004).

More recent research focuses on counter-insurgent conflicts, using new micro-level data and modeling techniques to address questions of counterinsurgent effectiveness in these complex conflicts. For example, Toft and Zhukov (2012) evaluated the effectiveness of denial versus punishment strategies, finding that denial (i.e., increasing the costs of expanding insurgent violence) is most effective, while punishment is counterproductive. Relatedly, Weidmann and Salehyan (2013) used an agent-based model applied to the U.S. surge in Baghdad to understand the mechanisms behind the surge’s success. They found that ethnic homogenization, rather than increased counterinsurgent capacity, best accounts for the surge’s success. Finally, Quackenbush and Murdie (2015) found that, counter to conventional wisdom, past experiences with counterinsurgency or conventional warfare have little effect on future success in conflict. States are not simply fighting the last war.

An important area of research that has fostered significant debate among scholars focuses on explaining the historical pattern of high rates of victory by democracies in interstate wars. The strongest explanations for the winning record of democracies center on their superior battlefield initiative and leadership, cooperative civil-military relations, and careful selection into wars they have a high probability of winning (Reiter & Stam, 2002). Challenging these results both theoretically and empirically, however, Desch (2002) argues that “democracy hardly matters,” that relative power plays a more important role in explaining victory. This debate essentially comes down to the relative importance of realist-type power variables versus regime type variables in explaining military victory; while scholars such as Lake (1992) and Reiter and Stam (2002) argued that regime type matters more, Desch asserted that relative power is the more important determinant of military victory.

Ultimately, we find Desch’s objections to the relevance of democracy to be overstated and his theoretical and empirical justifications to be largely unconvincing. First, Desch’s analysis is biased against Reiter and Stam’s argument because it is limited to dyads that Desch labels “fair fights,” that is, dyads with relatively equal military capabilities. This does not allow Desch to test the selection effect that Reiter and Stam discuss. Second, Desch failed to recognize that many of the realist variables he attributes the greatest explanatory power to are actually influenced by the foreign and military policies adopted by democratic leaders (Valentino et al., 2010). Democracy thus has both a direct and an indirect effect on war outcomes, and because Desch ignores the latter, he underestimates democracy’s total impact. Finally, the impacts of power variables may be overstated, as recent research demonstrates that military power’s influence is conditional upon method of force employment and military mechanization (Biddle, 2004; Lyall & Wilson, 2009).

More recent research examines some of the mechanisms suggested for the unique war-time behavior of democracies, raising some questions about existing mechanisms and suggesting alternatives to explain democratic exceptionalism. For example, Gibler and Miller (2013) argued that democracies tend to fight short, victorious wars because they have fewer territorial (i.e., high salience) issues over which to fight, rather than because of their leaders’ political accountability. Once controlling for issue salience, they find no relationship between democracy and victory. Similarly, using novel statistical techniques that allow them to account for the latent abilities of states, Renshon and Spirling (2015) showed that democracy only increases military effectiveness under certain conditions, and is actually counterproductive in others. Finally, new research by Bausch (2017) using laboratory experiments to test the mechanisms behind democracy and victory suggested that only some of these mechanisms hold up. Specifically, Bausch found that democratic leaders are actually more likely to select into conflict and do not mobilize more resources for war once involved, contrary to the selection and war fighting stories developed by Reiter and Stam (2002). He did find, however, that democratic leaders are less likely to accept settlement and more likely to fight to decisive victory once conflict is underway, and that democratic leaders are more likely to be punished than autocrats for losing a war. Thus, the debate over the democratic advantage in winning interstate wars continues to progress in productive directions.

Theoretical arguments regarding civil war outcomes focus on state/rebel strength, positing that factors such as natural resource wealth, state military capacity, and third-party assistance influence relative combatant strength and war outcomes. Empirical studies find that increasing state military strength decreases the likelihood of negotiated settlement and increases the probability of government victory (Mason et al., 1999). Characteristics of the war itself also affect outcomes, with the probability of negotiated settlement increasing as war duration increases (Mason et al., 1999; Walter, 2002), and high casualty rates increasing the likelihood of rebel victory (Mason et al., 1999).

Debate remains over how third-party interventions affect civil war outcomes. UN intervention decreases the likelihood of victory by either side while increasing the probability of negotiated war terminations (DeRouen & Sobek, 2004). This impact is time sensitive, however (Mason et al., 1999). Further, the impact of unilateral interventions is less clear. While Regan (1996) found intervention supporting the government to increase the likelihood of war termination, Gent (2008) found military intervention in support of rebels to increase their chance of victory but that in support of governments to have no significant impact. More recent research by Sullivan and Karreth (2015) helps explain this discrepancy. They argued that biased intervention only alters the chances for victory by the supported side if that side’s key deficiency is conventional war-fighting capacity. Empirically, they show that because rebels are generally weaker, military intervention on their behalf increases their chance of victory. For states, however, military intervention only increases their odds of victory if the state is militarily weaker than or at parity with the rebels.

Additional new research by Jones (2017) also represents an important step forward in understanding the effects of intervention in civil war. By examining both the timing and strategy of intervention, Jones demonstrated that the effects of intervention on conflict outcomes are much more complex than previous research suggests.

Post-War Peace Durability

As with studies on war duration, termination, and outcomes, much of the literature on the stability of post-war peace grows from extensions of the bargaining model of war. For these scholars, recurrence is most likely under conditions that encourage the renegotiation of the terms of settlement, including postwar changes in the balance of power (Werner, 1999) and externally forced ceasefires that artificially terminate fighting before both sides agree on the proper allocation of the spoils of war (Werner & Yuen, 2005). Building off of commitment problem models, Fortna (2004b) argued that strong peace agreements that enhance monitoring, incorporate punishment for defection, and reward cooperation help sustain peace. Specific measures within agreements, however, affect the durability of peace differently. For example, troop withdrawals and the establishment of demilitarized zones decrease the likelihood of war resumption, while arms control measures have no significant impact (Fortna, 2004b, p. 176).

Postwar intervention is also expected to increase peace duration by ameliorating commitment problems, as peacekeepers act as a physical barrier and reduce security fears, uncertainty, and misperceptions between former adversaries (Fortna, 2004a). Empirical results support this theoretical prediction, and while the size of the force is not significant, both monitoring and armed forces missions increase the durability of post-war peace (Fortna, 2004a).

The debate that remains in this literature is whether or not peace agreements can effectively mitigate the influence of relative power variables. Recent research by Lo, Hashimoto, and Reiter (2008) suggests that they cannot. They demonstrated that cease-fire agreement strength has almost no significant impact on post-war peace duration, while factors encouraging renegotiation receive partial support. While discrepancies in results may be in part attributable to differences in time periods covered, this result essentially confirms Warner and Yuen’s (2005) finding that externally imposed war termination invites resumption of conflict, regardless of the presence of strong cease-fire agreements.

If, at the end of a civil conflict, each side maintains its ability to wage war, issues of credibility can undermine the peace and cause the conflict to resume. Thus, wars ending in negotiated settlements are more likely to recur than those ending with a decisive victory because both sides have the ability to resume fighting to gain greater concessions and neither can credibly commit to the peace (Licklider,, 1995; Walter, 2002). More recent research confirms that conflicts ending in military victory are less likely to recur than those ending in settlement (Caplan & Hoeffler, 2017; Toft, 2009), though Toft suggested that this is particularly true for rebel victories.

This understanding of post-war peace in terms of the bargaining model’s commitment problem has led scholars to examine three primary avenues through which commitment problems might be overcome and peace maintained. First, partition has been advanced as a possible solution to post-war instability. The separation of warring factions is expected to reduce security fears by creating demographically separate, militarily defensible regions (Kaufmann, 1996). Empirical evidence generally supports this strategy. Partitions that successfully separate warring ethnic groups significantly reduce the risk of renewed conflict (Johnson, 2008), while those that do not achieve demographic separation increase the risk of renewed hostilities (Tir, 2005). Further, relative to de facto separation, autonomy arrangements, or maintenance of a unitary state, partition is significantly less likely to lead to war recurrence (Chapman & Roeder, 2007).

Second, third-party intervention is expected to play a role in ameliorating the security dilemma arising from commitment problems in post-conflict states (Fearon, 2004; Walter, 2002). Empirical results confirm that third-party security guarantees are critical to the signing and durability of peace settlements (Walter, 2002). Once settlement has been reached, third-party guarantees and international peacekeeping establish punishments for defection (Fortna, 2008; Walter, 2002), thereby reducing incentives for and increasing costs of renewed conflict. More recent research that employs more fine-grained data on the size and composition of UN peacekeeping forces suggests, however, that this type of third-party guarantee is most effective when it has the military power to enforce the peace. Specifically, Hultman, Kathman, and Shannon (2016) found that increasing UN troop presence increases peace durability, but the presence of other types of UN monitors has little effect on peace duration. By using more fine-grained data, this study makes an important contribution by allowing us to parse the mechanisms driving the role of third party guarantees in promoting peace.

Third, the incorporation of power-sharing arrangements that guarantee the survival of each side into the postwar settlement is also expected to solve post-civil war commitment problems (Walter, 2002). These arrangements allow adversaries to generate costly signals of their resolve to preserve the peace, thus ameliorating security fears (Hartzell & Hoddie, 2007). Empirical results indicate that given a negotiated settlement, the agreement’s ability to ameliorate security concerns is positively associated with the preservation of peace. Thus, the more regulation of coercive and political power included in an agreement, and the greater the number of dimensions (political, territorial, military, economic) of power sharing specified, the more likely agreements are to endure (Hartzell & Hoddie, 2007).

More recently, scholars have begun to extend this research by focusing more broadly on settlement design. Whereas previous research tended to simply count the number of power-sharing dimensions, newer analyses focus on issues such as the quality of the agreement (Badran, 2014) and equality in the terms of settlement (Albin & Druckman, 2012). Martin (2013), for example, found that provisions that share power at the executive level are less effective than those that regulate power at the level of rank-and-file or the public, as elite-level power-sharing is relatively easy for insincere actors to engage in at a relatively low cost. Cammett and Malesky (2012) found that proportional representation provisions are particularly effective at stabilizing post-conflict peace because of their ability to promote good governance and service provision, while Joshi and Mason (2011) similarly found that power-sharing provisions that expand the size of the governing coalition result in more stable peace. These analyses suggest that delving further into the design and content of settlement agreements is a positive avenue for future research. Future research should also examine how implementation of peace agreements proceeds, and how the timing and sequencing of implementation affects the durability of peace (e.g., Langer & Brown, 2016).

Finally, emerging research on civil war recurrence also shifts focus toward rebel groups and how their composition and integration affect post-conflict peace. For example, new research finds that rebel group fragmentation hastens the recurrence of civil war (Rudloff & Findley, 2016), while greater inclusion of former rebels in government improves prospects for post-conflict peace (Call, 2012; Marshall & Ishiyama, 2016). Emerging research on post-conflict elections also represents an important area for further study, as debate remains over how elections affect conflict recurrence. While some argue that they destabilize the peace (Flores & Nooruddin, 2012), others suggest they actually reduce the risk of conflict recurrence (Matanock, 2017).

The Longer-Term Consequences of Wars

What are the political, economic, and social consequences of interstate and civil wars, and what explains these postwar conditions? As Rasler and Thompson (1992) recognized, the consequences of war are often far-reaching and complex. Given this complexity, much of the literature varies significantly in quality and coverage; while post-war political change has received significant attention from political scientists, the social and health-related consequences of war are less well-known.

Post-War Domestic Political Stability and Change

Scholarship on post-war political stability focuses on both regime and leadership change, positing political accountability as a central mechanism in both cases. Interstate war has been theorized to induce internal revolution both indirectly (Skocpol, 1979) and directly (Bueno De Mesquita et al., 2003; Goemans, 2000). Empirical results support the accountability argument, as war losses and increasing costs of war increase the likelihood of post-war leadership turnover (Bueno De Mesquita & Siverson, 1995) as well as violent regime overthrow (Bueno De Mesquita, Siverson, & Woller, 1992). Related work shows that accountable leaders are also more likely to face foreign-imposed regime change at the hands of war victors (Bueno De Mesquita et al., 2003).

A central focus of recent research has been the conditional relationship between war outcomes and regime type. In his seminal study, Goemans, 2000) found that leaders of mixed and democratic regimes are more likely to be removed from office as a result of moderate losses in war than are leaders of autocracies. These findings, however, have been challenged by recent scholarship. Colaresi (2004) finds no difference in leadership turnover rates across all regimes types under conditions of moderate war losses, and Chiozza and Goemans (2004), employing a different measure of war outcomes and discounting the impact of termination over time, find that defeat in war is most costly for autocratic leaders and has no significant impact on tenure for democratic leaders.

Recently, research in the civil war literature has begun to focus more on post-war democratization, elections, and how groups transition from fighting forces to political parties. Much of the early work in this area focused on the link between war outcomes and the development of democratic institutions in the post-war period, specifically arguing that negotiated settlements facilitate democratization by requiring the inclusion of opposition groups in the decision-making process (Doyle & Sambanis, 2006; Gurses & Mason, 2008). More recent research, however, challenges this conventional wisdom, showing that the benefits of negotiated settlement are limited to the short-term and that economic factors are better predictors of post-war democratization (Fortna & Huang, 2012).

Recognizing that not all negotiated settlements are created equal, scholars have also begun to examine how variation in power-sharing provisions influences democratization. Debate remains on this topic as well, however. While some argue that power-sharing facilitates democratization by generating costly signals that create the stability necessary for democratization (Hoddie & Hartzell, 2005), others argue that they undermine democratization by reifying wartime cleavages, incentivizing political parties to seek support only from their own wartime constituencies, and undermining public confidence in governmental institutions (Jung, 2012). However, after accounting for non-random selection into power-sharing, Hartzell and Hoddie (2015) found that the inclusion of multiple power-sharing provisions in peace agreements increases post-civil war democratization. Future research should delve further into this debate, and consider more carefully whether specific types of provisions or institutional designs vary in their ability to promote democracy. Joshi (2013) represents an important first step in this direction, finding that institutional designs that favor inclusivity (e.g., parliamentary systems and proportional representation) are more successful at producing democracy.

Debate also continues over the effects of international intervention on post-conflict democratization. While some scholars expect intervention to facilitate postwar democratization by mitigating commitment problems and raising the costs of defection (Doyle & Sambanis, 2006), others suggest it is used as a tool by interveners to impose amenable, generally non-democratic, institutions in the target country (Bueno De Mesquita & Downs, 2006). Doyle and Sambanis (2006) found multidimensional UN missions incorporating economic reconstruction, institutional reform, and election oversight, to be significantly and positively correlated with the development of postwar democracy. However, Gurses and Mason (2008) and Fortna and Huang (2012) challenged this finding, reporting no significant relationship between UN presence and postwar democratization, and Paris (2004) and Bueno de Mesquita and Downs (2006) showed that peacebuilding missions and UN interventions actually decrease levels of democracy.

Future research should attempt to reconcile many of these open debates in both the interstate and civil conflict literatures. It should also build upon emerging research on post-conflict elections (Flores & Nooruddin, 2012; Matanock, 2017) and rebel governance (Huang, 2016). Huang’s work on rebel governance, in particular, shows that how rebels interact with civilian populations during conflict has important implications for post-conflict democratization.

Public Health Conditions in the Aftermath of Wars

Social scientists have recently begun to study the consequences of war for the postwar health and well-being of civilian populations. Theoretical arguments developed in this literature generally do not distinguish between interstate and civil war, instead developing mechanisms that apply to both types of conflict. The most direct public health consequence of war, of course, results from the killing and wounding of civilian populations. Scholars argue, however, that more indirect mechanisms cause longer-term public health problems as well. War, for example, is expected to undermine long-term public health by exposing populations to hazardous conditions through the movement of refugees and soldiers as vectors for disease (Ghobarah, Huth, & Russett, 2003; Iqbal, 2006), damaging health-related facilities and basic infrastructure (Li & Wen, 2005; Plümper & Neumayer, 2006), and reducing government spending and private investment on public health (Ghobarah et al., 2003).

Many empirical analyses, unfortunately, do not directly address the mechanisms outlined above. Overall, findings indicate that both civil and interstate war increase adult mortality in the short and long term (Li & Wen, 2005) and decrease health-adjusted life-expectancy in the short term (Iqbal, 2006). Conflict severity is also influential; while low-level conflict has no significant effect on mortality rates, severe conflict increases mortality and decreases life-expectancy in the long run (Li & Wen, 2005; Hoddie & Smith, 2009; Iqbal, 2006). Comparing the health impacts of interstate and civil wars, analysts have found interstate conflict to exert a stronger, negative impact on long-term mortality rates than civil war, despite the finding that civil war’s immediate impact is more severe (Li & Wen, 2005). Finally, many analysts have found that the negative, long-term effects of war are consistently stronger for women and children (Ghobarah, et al., 2003; Plümper & Neumayer (2006) than for men.

This developing field provides important new insights into the civilian consequences of war, but remains underdeveloped in many respects. First, while some evidence suggests that civil and interstate war might affect public health differently, the mechanisms behind these differences require further elaboration. Research by Hoddie and Smith, represented an important contribution in this respect, as it distinguishes between different conflict strategies, finding that conflicts involving extensive violence against noncombatants have more severe health consequences than those in which most fatalities are combat-related. Second, theoretical models are generally much more developed and sophisticated than the data used to test them. While data availability is limited, efforts should be made to more closely match theory and empirics.

Third, analyses that employ disaggregated measures of health consequences (Ghobarah et al., 2003) provided a more thorough understanding of the specific consequences of war and represent an important avenue for additional theoretical and empirical development. Iqbal and Zorn (2010) thus focus specifically on conflict’s detrimental impact on the transmission of HIV/AIDS, while Iqbal (2010) examines the impact of conflict on many different health-based metrics, including infant mortality, health-associated life expectancy, fertility rates, and even measles and diphtheria vaccination rates. These studies represent important advances in the literature, which should be explored further in future research to disentangle the potentially complex health effects of civil and interstate conflict.

Finally, recent research has begun to conceptualize health more broadly, accounting for the psychological consequences of wartime violence. Building upon research in psychology, Koos (2018) finds that exposure to conflict-related sexual violence in Sierra Leone generates resilience: affected households display greater cooperation and altruism than those unaffected by such violence during conflict. Bauer et al. (2016) similarly find that conflict fosters greater social cohesion and civic engagement in the aftermath of war. This is an important area for future research. As conceptions of conflict-related violence broaden, our conceptualizations of the consequences of violence should also expand to include notions of how conflict affects psychological health, community cohesion, and other less direct indicators of public health.

Conclusion

This final section highlights some of the contributions generated by scholarship on the conduct and consequences of war, as well as some of the gaps that remain to be addressed. First, this body of scholarship usefully compliments the large and more traditional work of military historians who study international wars, as well as the work of contemporary defense analysts who conduct careful policy analyses on relevant issues such as wartime military tactics and strategy as well as weapon system performance. The bargaining model of war has also proven a useful theoretical framework in which to structure and integrate theoretical analyses across different stages in the evolution of war.

Second, a number of studies in this body of work have contributed to the further development and testing of the democratic peace literature by extending the logic of political accountability models from questions of war onset to democratic wartime behavior. New dependent variables, including civilian targeting, imposition of regime change, the waging of war in ways designed to reduce military and civilian losses, and victory versus defeat in war have been analyzed. As a result, a number of new arguments and empirical findings have improved our understanding of how major security policy decisions by democratic leaders are influenced by domestic politics.

Third, this literature has advanced scholarship on international law and institutions by examining questions about compliance with the laws of war and the role played by the UN in terminating wars and maintaining a durable post-war peace. The impact of international law and institutions is much better understood on issues relating to international political economy, human rights, and international environmental governance than it is on international security affairs. As a result, studies of compliance with the laws of war, the design of ceasefire agreements, or international peace-building efforts address major gaps in existing literature.

Fourth, this new body of research has explicitly focused on the consequences of war for civilian populations, a relatively neglected topic in academic research. Research on questions such as the deliberate targeting of civilians during wars and the longer-term health consequences of war begin to address this surprising gap in research. As such, this new literature subjects the study of terrorism to more systematic social science methods and also challenges the common practice of restricting terrorism to non-state actors and groups when, in fact, governments have resorted to terrorist attacks on many occasions in the waging of war.

While this literature has advanced scholarship in many ways, there remain several theoretical and empirical gaps that future research should aim to address, two of which are highlighted here. First, while research on interstate war duration and termination is more theoretically unified than its civil war counterpart, the dominance of the bargaining model in this literature is currently being challenged. Recent research on asymmetric conflict suggests that the basic tenants of the bargaining model may not hold for non-symmetric conflict, while research on force employment and mechanization suggest that traditional power measures exert a conditional impact at best. Additional research is needed to determine the conditions under which bargaining logic applies and its relative importance in explaining wartime behavior and war outcomes.

Second, the accumulation of knowledge on civil war’s conduct and consequences has lagged behind that on interstate war, partially because the civil war literature is younger, and partially because sub-national level data is only now becoming more readily available. While bargaining logic is often applied to civil war, we have little cross-national information on relative capabilities and battle trends, and thus a very limited understanding of the way in which these variables affect civil war duration and outcomes. New micro-level data and studies that are beginning to address these problems represent a promising direction forward for civil conflict research.

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