Introduction

The idea of balance of power in international politics arose during the Renaissance age as a metaphorical concept borrowed from other fields (ethics, the arts, philosophy, law, medicine, economics, and the sciences), where balancing and its relation to equipoise and counterweight had already gained broad acceptance. Wherever it was applied, the “balance” metaphor was conceived as a law of nature underlying most things we find appealing, whether order, peace, justice, fairness, moderation, symmetry, harmony, or beauty.¹ In the words of Jean-Jacques Rousseau: “The balance existing between the power of these diverse members of the European society is more the work of nature than of art. It maintains itself without effort, in such a manner that if it sinks on one side, it reestablishes itself very soon on the other.”²

Centuries later, this Renaissance image of balance as an automatic response driven by a law of nature still suffuses analysis of how the theory operates within the sphere of international relations. Thus, Hans Morgenthau explained, “The aspiration for power on the part of several nations, each trying either to maintain or overthrow the status quo, leads of necessity, to a configuration that is called the balance of power and to policies that aim at preserving it.”³ Similarly, Kenneth Waltz declared, “As nature abhors a vacuum, so international politics abhors unbalanced power.”⁴ Christopher Layne likewise avers, “Great powers balance against each other because structural constraints impel them to do so.”⁵ Realists, such as Arnold Wolfers, invoke the same “law of nature” metaphor to explain opportunistic expansion: “Since nations, like nature, are said to abhor a vacuum, one could predict that the powerful nation would feel compelled to fill the vacuum with its own power.”⁶ Using similar structural-incentives-for-gains logic, John Mearsheimer claims that “status quo powers are rarely found in world politics, because the international system creates powerful incentives for states to look for opportunities to gain power at the expense of rivals, and to take advantage of those situations when the benefits outweigh the costs.”⁷

From the policymaker’s perspective, however, balancing superior power and filling power vacuums hardly appear as laws of nature. Instead, these behaviors, which carry considerable political costs and uncertain policy risks, emerge through the medium of the political process; as such, they are the product of competition and consensus-building among elites with differing ideas about the political-military world and divergent views on the nation’s goals and challenges and the means that will best serve those purposes.⁸ As Nicholas Spykman observed many years ago, “political equilibrium is neither a gift of the gods nor an inherently stable condition. It results from the active intervention of man, from the operation of political forces. States cannot afford to wait passively for the happy time when a miraculously achieved balance of power will bring peace and security. If they wish to survive, they must be willing to go to war to preserve a balance against the growing hegemonic power of the period.”⁹

In an era of mass politics, the decision to check unbalanced power by means of arms and allies—and to go to war if these deterrent measures fail—is very much a political act made by political actors. War mobilization and fighting are distinctly collective undertakings. As such, political elites must weigh the likely domestic costs of balancing behavior against the alternative means available to them and the expected benefits of a restored balance of power. Leaders are rarely, if ever, compelled by structural imperatives to adopt certain policies rather than others; they are not sleepwalkers buffeted about by inexorable forces beyond their control. This is not to suggest that they are oblivious to the constraints imposed by international structure. Rather, systemic pressures are filtered through intervening variables at the domestic level to produce foreign policy behaviors. Thus, states respond (or not) to power shifts—and the threats and opportunities they present—in various ways that are determined by both internal and external considerations of policy elites, who must reach consensus within an often decentralized and competitive political process.¹⁰

Meanings of Balance of Power and Balancing Behavior

While the balance of power is arguably the oldest and most familiar theory of international politics, it remains fraught with conceptual ambiguities and competing theoretical and empirical claims.¹¹ Among its various meanings are (a) an even distribution of power; (b) the principle that power ought to be evenly distributed; (c) the existing distribution of power as a synonym for the prevailing political situation; that is, any possible distribution of power that exists at a particular time; (d) the principle of equal aggrandizement of the great powers at the expense of the weak; (e) the principle that our side ought to have a preponderance of power to prevent the danger of power becoming evenly distributed; in this view, a power “balance” is likened to a bank balance, that is, a surplus rather than equality; (f) a situation that exists when one state possesses the special role of holding the balance (called the balancer) and thereby maintains an even distribution of power between two rival sides; and (g) an inherent tendency of international politics to produce an even distribution of power.

The conceptual murkiness surrounding the theory extends to its core concept, balancing behavior. What precisely does the term “balancing” mean? Some scholars talk about soft balancing,¹² others have added psycho-cultural balancing, political-diplomatic balancing, and strategic balancing,¹³ while still others talk about economic and ideological balancing.¹⁴ Because balance of power is a theory about international security and preparations for possible war, I offer the following definition of balancing centered on military capabilities: “Balancing means the creation or aggregation of military power through either internal mobilization or the forging of alliances to prevent or deter the occupation and domination of the state by a foreign power or coalition. The state balances to prevent the loss of territory, either one’s homeland or vital interests abroad (e.g., sea lanes, colonies, or other territory considered of vital strategic interest). Balancing only exists when states target their military hardware at each other in preparation for a possible war. If two states are merely building arms for the purpose of independent action against third parties, we cannot say that they are engaged in balancing behavior. State A may be building up its military power and even targeting another state B and still not be balancing against B, that is, trying to match B’s overall capabilities with the aim of possible territorial conquest or preventing such conquest by B. Instead, the purpose may be coercive diplomacy: to gain bargaining leverage with state B.”¹⁵

The Goals, Means, and Dynamics of Balance of Power

International relations theorists have exhibited remarkable ambiguity about not only the meaning of balance of power but the results to be expected from a successfully operating balance of power system.¹⁶ What is the ultimate promise of balance of power theory? The purpose or goal of balance of power—if such a thing can be attributed to an unintended spontaneously generated order—is not the maintenance of international peace and stability, as many of the theory’s detractors have wrongly asserted. Rather it is to preserve the integrity of the multistate system by preventing any ambitious state from swallowing up its neighbors. The basic intuition behind the theory is that states are not to be trusted with inordinate power, which threatens all members of the international system. The danger is that a predatory great power might gain more than half of the total resources of the system and thereby be in position to subjugate all the rest.

It is further assumed that the only truly effective and reliable antidote to power is power. Increases in power (especially a rival’s growing strength), therefore, must be checked by countervailing power. The means of accomplishing this aim are arms and allies: states counterbalance threatening accumulations of power by building arms (internal balancing) and forming alliances (external balancing) that serve to aggregate each other’s military power. Because the “balance of power” primarily refers to the relative power capabilities of great power rivals and opponents (it is, after all, a theory about great powers, the primary actors in international politics) in the event of war between them, fighting power is the power to be gauged. In determining what capabilities to measure, context is crucial: “To test a theory in various historical and temporal contexts requires equivalent, not identical, measures.”¹⁷ An accurate assessment of the balance of power must include (a) the military capabilities (the means of destruction) each holds and can draw upon; (b) the political capacity to extract and apply those capabilities; (c) the capabilities and reliability of commitments of allies and possible allies; and (d) the basic features of the political geography (viz., the military and political consequences of the relationships between physical geography, state territories, and state power) of the conflict.¹⁸ While the exact components of any particular power capability index will vary, they typically include combinations of the following measures: land area (territorial size), total population, size of armed forces, defense expenditures, overall and per capita size of the economy (e.g., gross national product), technological development (which includes measures such as steel production and fossil fuel consumption), per capita value of international trade, government revenue, and less easily measured capabilities such as political will and competence, combat efficiency, and the like.

In summary, balance of power’s general principle of action may be put as follows: when any state or coalition becomes or threatens to become inordinately powerful, other states should recognize this as a threat to their security (sometimes to their very survival) and respond by taking measures—individually or jointly or both—to enhance their military power. This process of equilibration is thought to be the central operational rule of the system. There is disagreement, however, over how the process, in practice, actually works; that is, over the degree of conscious motivation required for the production of equilibrium. Along these lines, Claude provides three types of balance of power systems: the automatic version, which is self-regulating and spontaneously generated; the semi-automatic version, whereby equilibrium requires a “balancer”—throwing its weight on one side of the scale or the other, depending on which is lighter—to regulate the system; and the manually operated version, wherein the process of equilibrium is a function of human contrivance, with emphasis on the skill of diplomats and statesmen who carefully manage the affairs of the units (states and other non-state territories) constituting the system.

The manually operated balance of power system is consistent with the English School’s notion that states consider balance as something of a collective good. The role of great power comes with the responsibility to maintain the balance of power. It is “a conception of the balance of power as a state of affairs brought about not merely by conscious policies of particular states that oppose preponderance throughout all the reaches of the system, but as a conscious goal of the system as a whole.”¹⁹

Nine Conditions that Promote the Smooth Operation of the Balance of Power

Recognizing the confusion and flexibility attending the term “balance of power,” any attempt to construct a list of conditions that make a balance of power system most likely to emerge, endure, and function properly should be seen as a worthy, if not foolhardy, exercise. In that spirit, I offer the following nine conditions, which are jointly sufficient to bring about an effectively performing balance-of-power system.

The Balance of Power as an International Order

At its essence, balance of power is a type of international order. What do we mean by an international order? A system exhibits “order” when the set of discrete objects that comprise the system are related to one another according to some pattern; that is, their relationship is not miscellaneous or haphazard but accords with some discernible principle. Order prevails when things display a high degree of predictability, when there are regularities, when there are patterns that follow some understandable and consistent logic. Disorder is a condition of randomness—of unpredictable developments lacking regularities and following no known principle or logic. The degree of order exhibited by social and political systems is partly a function of stability. Stability is the property of a system that causes it to return to its original condition after it has been disturbed from a state of equilibrium. Systems are said to be unstable when slight disturbances produce large disruptions that not only prevent the original condition from being restored but also amplify the effect of the perturbation. This process is called “positive feedback,” because it pushes the system increasingly farther away from its initial steady state. The classic example of positive feedback is a bank run caused by self-fulfilling prophesies: people believe something is true (there will be a run on the bank), so their behavior makes it true (they all withdraw their money from the bank); and others’ observations of this behavior increases the belief that it is true, so they behave accordingly (they, too, withdraw their money from the bank), which makes the prophesy even more true, and so on.³³

Some systems are characterized by robust and durable orders. Others are extremely unstable, such that their orders can quickly and without warning collapse into chaos. Like an avalanche, or peaks of sand in an hourglass that suddenly collapse and cascade, or a spider web that takes on an entirely new pattern when a single strand is cut, complex and delicately balanced systems are unpredictable: they may appear calm and orderly at one moment only to become wildly turbulent and disorderly the next. This inherent instability of complex, tightly coupled systems is captured by the popular catch phrase, “the butterfly effect,” coined by the MIT meteorologist, Edward Lorenz, to explain how a massive storm can be caused (or prevented) by the faraway flapping of a tiny butterfly’s wings. The principal lesson of the butterfly effect is that, when incalculably small differences in the initial conditions of a system matter greatly, the world becomes radically unpredictable.³⁴ Indeed, we can seldom predict what will happen when a new element is added to a system composed of many parts connected in complex ways. Such systems undergo frequent discontinuous changes from shocking impacts that create radical departures from the past.

International orders vary according to (a) the amount of order displayed; (b) whether the order is purposive or unintended; and (c) the type of mechanisms that provide order. On one end of the spectrum, there is rule-governed, purposive order, which is explicitly designed and highly institutionalized to fulfill universally accepted social ends and values.³⁵ At the other extreme, international order is an entirely unintended and un-institutionalized recurrent pattern (e.g., a balance of power) to which the actors and the system itself exhibit conformity but which serves none of the actors’ goals or which, at least, was not deliberately designed to do so. Here, international order is spontaneously generated and self-regulating. The classic example of this spontaneously generated order is the balance of power, which arises though none of the states may seek equality of power; to the contrary, all actors may seek greater power than everyone else, but the concussion of their actions (which aim to maximize their power) produces the unintended consequence of a balance of power.³⁶ In other words, the actors are constrained by a system that is the unintended product of their coactions (akin to the invisible hand of the market, which is a spontaneously generated order/system).

There are essentially three types of international orders:

The predictability of a social system depends, among other things, on its degree of complexity, whether its essential mechanisms are automatic or volitional, and whether the system requires key members to act against their short-run interests in order to work properly. Negotiated (sometimes referred to as “constitutional”) orders are complex systems that rely on ad hoc human choices and require actors to choose voluntarily to subordinate their immediate interests to communal or remote ones (e.g., in collective security systems). As such, how they actually perform when confronted with a disturbance that trips the alarm, so to speak, will be highly unpredictable. In contrast, the operation of a balance-of-power system is fairly automatic and therefore highly predictable. It simply requires that states, seeking to survive and thrive in a competitive, self-help realm, pursue their short-run interests; that is, states seek power and security, as they must in an anarchic order.³⁸

Here, I do not mean to suggest that balance-of-power systems always function properly and predictably. Balancing can be late, uncertain, or nonexistent. These types of balancing maladies, however, typically occur when states consciously seek to opt out of a balance-of-power system, as happened in the interwar period, but then fail to replace it with a functioning alternative security system. The result is that a balance-of-power order, which may be viewed as a default system that arises spontaneously, in the absence or failure of concerted arrangements among all the units of the system to provide for their collective security, eventually emerges but is not accomplished as efficiently as it otherwise would have been.

Does Balancing Behavior Prevail Over Other State Responses to Growing Power?

There have been several recent challenges to the conventional realist wisdom that balancing is more prevalent than bandwagoning behavior, that is, when states join the stronger or more threatening side.³⁹ Paul Schroeder’s broad historical survey of international politics shows that states have bandwagoned with or hid from threats far more often than they have balanced against them. Similarly, I have claimed that bandwagoning behavior is more prevalent than contemporary realists have led us to believe because alliances among revisionist states, whose behavior has been ignored by modern realists, are driven by the search for profit, not security.⁴⁰ Most recently, Robert Powell treats states as rational unitary actors within a simple strategic setting composed of commitment issues, informational problems, and the technology of coercion and finds that “balancing is relatively rare in the model. Balances of power sometimes form, but there is no general tendency toward this outcome. Nor do states generally balance against threats. States frequently wait, bandwagon, or, much less often, balance.”⁴¹ Powell freely admits, however, that a rational-unitary-actor assumption “does not mean that domestic politics is unimportant.”⁴² None of these studies, however, has offered a domestic-politics explanation for bandwagoning or a theory of the broader phenomenon of underbalancing behavior, which includes buck-passing, distancing, hiding, waiting, appeasement, bandwagoning, incoherent half-measures, and, in extreme cases, civil war, revolution, and state disintegration.

In addition to studies of bandwagoning, there has been some work on what is called “buck-passing” behavior, a form of under-reaction to threats by which states attempt to ride free on the balancing efforts of others. Two popular explanations for buck-passing behavior are structural-systemic ones. Thomas Christensen and Jack Snyder claim that great powers under multipolarity will buck-pass when they perceive defensive advantage; while John Mearsheimer argues that buck-passing occurs primarily in balanced multipolar systems, especially among great powers that are geographically insulated from the aggressor.⁴³ Others argue that whether or not states balance against threats is not primarily determined by systemic factors but rather by domestic political processes.⁴⁴

Along these lines, it is important to point out that, when we speak of balancing and other competing responses to growing power, we are actually referring to four distinct categories of behavior. First, there is appropriate balancing, which occurs when the target is a truly dangerous aggressor that cannot or should not be appeased. Second, there is inappropriate balancing, which unnecessarily triggers a costly and dangerous arms spiral because the target is misperceived as an aggressor but is, in fact, a defensively minded state seeking only to enhance its security.⁴⁵ Third, there is nonbalancing, which may take the form of buck-passing, bandwagoning, appeasement, engagement, distancing, or hiding. These policies may be quite prudent and rational when the state is thereby able to avoid the costs of war either by satisfying the legitimate grievances of the revisionist state or allowing others to satisfy them, or by letting others defeat the aggressor while safely remaining on the sidelines. Moreover, if the state also seeks revision, then it may wisely choose to bandwagon with the potential aggressor in the hope of profiting from its success in overturning the established order. Finally, there is an unusual state of affairs, such as those we live under today, in which one state is so overwhelmingly powerful that there can be said to exist an actual harmony of interests between the hegemon (or unipole) and the rest of the great powers—those that could either one day become peer competitors or join together to balance against the predominant power. The other states do not balance against the hegemon because they are too weak (individually and collectively) and, more important, because they perceive their well being as inextricably tied up with the well-being of the hegemon. Here, potential “balancers” bandwagon with the hegemon not because they seek to overthrow the established order (the motive for revisionist bandwagoning), but because they perceive themselves to be benefiting from the status-quo order and, therefore, seek to preserve it.⁴⁶

Finally, there is underbalancing, which occurs when the state does not balance or does so inefficiently in response to a dangerous and unappeasable aggressor, and the state’s efforts are absolutely essential to deter or defeat it. In these cases, the underbalancing state not only does not avoid the costs of war but also brings about a war that could have been avoided or makes the war more costly than it otherwise would have been or both.⁴⁷

Criticisms of Balance-of-Power Theory

Since the end of the Cold War, many scholars of international politics have come to believe that realism and the balance of power are now obsolete. Liberal critics charge that, while power balancing may have been appropriate to a bygone era, international politics has been transformed as democracy extends its sway, as interdependence tightens its grip, and as institutions smooth the way to peace. If other states do arise over the coming decades to become peer competitors of the United States, the world will not return to a multipolar balance of power system but rather will enter a new multipartner phase. In the words of Secretary of State Hillary Clinton, “It does not make sense to adapt a 19th-century concert of powers or a 20th-century balance-of-power strategy. We cannot go back to Cold War containment or to unilateralism,” she said in a speech at the Council on Foreign Relations in July 2009. “We will lead by inducing greater cooperation among a greater number of actors and reducing competition, tilting the balance away from a multipolar world and toward a multipartner world.”⁴⁸

It is a view based on the assumption that history moves forward in a progressive direction—one consistent with the metaphor of time’s arrow.⁴⁹ Of course, realists have heard all this before. Consider Woodrow Wilson’s description of pre-World War I Europe: “The day we left behind us was a day of alliances. It was a day of balances of power. It was a day of ‘every nation take care of itself or make a partnership with some other nation or group of nations to hold the peace of the world steady or to dominate the weaker portions of the world’.”⁵⁰

While I suspect that social constructivists would agree with most (if not all) of the arguments posed by the liberal challenge to realism, the thrust of their attack is more conceptual and theoretically oriented. As mentioned, Stephen Walt’s “balance of threat” theory, by including “aggressive intentions” as a dimension of threat, widens the stimuli to which states perceive dangers to include more than just material power. Social constructivists, like Michael Barnett, charge that Walt, having shattered neorealist theory, does not go far enough in defining the ideational elements that determine threats and alliances. Ideology and ideas about identity and norms are, according to social constructivists, often the most important sources of threat perception, as well as the primary basis for alliance formation itself.⁵¹

Finally, even self-described realists wonder if balance of power still operates in the contemporary world, at least at the global level. For various “sound realist” reasons, Stephen Brooks and William Wohlforth see a world out of balance—one in which the United States maintains its unchallenged global primacy for another 20 years or more.⁵² Edward Rhodes goes farther, urging the field to abandon, rather than hopelessly attempting to rehabilitate, the “balancing” metaphor and the logic that flows from it. Balancing behavior, he claims, makes no sense in a world devoid of “trinitarian wars” and the belief that any state, if too powerful and unchecked by other states, threatens the sovereignty of all other states. Today, nuclear arsenals assure great powers of the ultimate invulnerability of their sovereignty.⁵³ Moreover, war among the great powers in the present age is, if not downright ludicrous and unthinkable, far from an expected and sensible means to resolve their disputes. Balance of power is a theory deeply rooted in a territorial view of wealth and security—a world that no longer exists.⁵⁴