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date: 28 October 2020

Internalization of International Lawfree

  • Dana ZartnerDana ZartnerInternational Studies Department, University of San Francisco


The internalization of international is the process by which nations incorporate international law domestically. While ratifying an international treaty or accepting a principle of customary international law technically binds a state to follow the rule, it is widely understood that, for international law to be implemented correctly, it must be internalized domestically because actors must have some binding sense of obligation to the law before it becomes viewed as the appropriate standard of behavior. The internalization of international law into domestic law can involve formal international laws, such as the provisions of a treaty or refer to the incorporation of broader international norms, whether or not they are codified in written form. A wide range of cultural and institutional factors can either facilitate or hinder the internalization of international law. Cultural factors include the purpose of law, the origins of the law, and perceptions of appropriate standards of behavior. Institutional factors include whether the state is monist or dualist, the political structure of the various branches of government, and the role and power of the judiciary.


  • International Law

Updated in this version

Updated references; light revision throughout.

Introduction: What Is Internalization?

The internalization of international law into the domestic law of a state has been an area of scholarship that has traditionally not received widespread attention from scholars of international relations (Dunoff & Pollack, 2013). This has begun to change over the last few years as more scholars recognize that internalization is a key component of our understanding of the role that international law plays in shaping state behavior (Powell, 2020; Zartner, 2014). Grounded in the fields of international law and international relations, the internalization of international law into a state’s domestic law is a key component by which international law becomes, not only binding on states, but also capable of shifting public understandings about changing global norms and acceptable behaviors. An international legal principle agreed upon by states at the international system level requires some mechanism by which the legal norms become integrated into the understanding of what is the appropriate and lawful behavior at the domestic level. As domestic law is grounded in culturally relevant legal norms and institutions—for example, grounded in the Constitution in the United States—so must international law become grounded to reach the level of opinio juris sive necessitatis, or obligation, which is necessary to shape state action. Moreover, as international law has broadened its scope to an increasing number of subjects and to an increasing number of actors, understanding the impact that internalization of international law into domestic law may have on behavior furthers our understanding of the guiding force of international law and the effect international law has, not only on states, but on nonstate actors operating within a state.

To further our understanding of the role that internalization plays in the compliance with, and effectiveness of, international law, this article addresses a number of issues. First, it provides definitions for the concepts of internalization and international law and discusses the importance of understanding how international law is internalized for our broader understanding of international relations. The focus is primarily on the role of internalization in solidifying acceptance of international legal rules and facilitating state compliance with international law. Second, the internalization of international law is briefly examined in the context of several of the main theoretical approaches in international relations. Third, the process of internalization itself is considered, along with the institutional and normative factors that facilitate internalization of international law into domestic law. Finally, the article briefly addresses some of the key questions that remain to be addressed on this subject and what examination of these questions may be able to illuminate in terms of state and nonstate actors’ behavior toward international law.

Internalization: Integral to Compliance

Definition of Internalization and Importance to Understanding Compliance

The internalization of international law is defined as “the process by which nations incorporate international law concepts into domestic practice” (Cleveland, 2001). International law is created and agreed to by states at the international system level. While ratifying an international treaty or accepting a principle of customary international law technically binds a state to follow the rule, it is widely understood that, for international law to be implemented correctly, it must be internalized domestically (Cohen, 2005; Koh, 1997; Zartner, 2014). This is because actors, whether elites working in the government or individual citizens, must have some binding sense of obligation to the law before it becomes viewed as the appropriate standard of behavior (see March & Olson, 1998 on the “logic of appropriateness”).

This need for understanding the appropriate standard of behavior is true at the domestic level as well as at the international level, and can occur in a number of different ways involving both state and nonstate actors. For example, in the United States, law that is passed by Congress must be viewed as constitutionally valid for it to be accepted as law. If a law or regulation is perceived as being in violation of the U.S. Constitution, under our domestic system of law, that law is viewed with suspicion until either upheld or struck down by a court. In other countries, law may not be considered valid until it receives the approval of a religious council or is integrated into customary practice (Zartner, 2014).

In addition to cultural perceptions of the appropriate standards of behavior influencing internalization, hierarchies of law may also play a role. The prominence a state gives to certain sources of domestic law may hinder the acceptance and internalization of international legal norms that are seen as infringing on, or contradicting, the revered domestic sources. States like the United States, that hold their constitution as the supreme law of the land, as well as states where religious law forms the foundation of their legal tradition view international law as secondary in the hierarchy of sources of law (Zartner, 2014). In either case, though, the point remains the same: Law requires internalization and grounding in societal culture for it to be held as binding. Moreover, internalization provides enforcement mechanisms to ensure the law is followed. If a law is not recognized as binding or as mandating the appropriate standards of behavior, then there is less chance that the law will be seen has binding and a greater likelihood the rule will not be followed out of a sense of obligation. This becomes more important at the international system level, where enforcement mechanisms are even less concrete.

The internalization of international law into domestic law can involve formal international laws such as the provisions of a treaty. Internalization can also refer to the incorporation of broader international norms, whether or not codified in written form, into the normative structure of the state. For internalization to be successful, therefore, it is important to consider the type of international law at issue, as well as the legal, political, social, and cultural aspects of states, which may facilitate or hinder the internalization process (Finnemore & Sikkink, 1998; Rosenblum, 2006; Zartner, 2014). For many years, customary international law was internalized more readily, as it was considered part of the broader normative body of law and its nonwritten provisions were easier to internalize. This idea was epitomized in the United States Supreme Court case, The Paquete Habana, in which the Court wrote:

International law is part of our law, and must be ascertained and administered by the courts of justice of appropriate jurisdiction. . . [W]here there is no treaty, and no controlling executive or legislative act or judicial decision, resort must be had to the customs and usages of . . . nations. . .

(U.S. Supreme Court, 1900)

It has also been argued that customary international law is viewed as less Western-dominated than many of the international treaties that are drafted (Chimni, 2018). This means that for many states in the Global South internalizing principles of customary international law “face less resistance from subaltern groups and states” (Chimni, 2018, p. 9).

In general, however, as the use of customary international law has decreased in favor of the codification of norms in bilateral and multilateral treaties, difficulties with internalization have increased relative to the more specific nature of treaties.

Definition of International Law

International law is defined somewhat differently by international lawyers and international relations theorists. For international lawyers, international law can be defined as “the body of rules and principles of action which are binding upon civilized states in their relations with one another” (Wood, 2000). This definition of international law is further specified in Article 38 of the Statute of the International Court of Justice, which lists the following as binding international law:

International conventions, whether general or particular, establishing rules expressly recognized by the contesting states.

International custom, as evidence of a general practice accepted as law.

The general principles of law recognized by civilized nations.

Subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.

For international lawyers, therefore, what encompass international law are very specific sources considered binding rules, whether in the form of a treaty or a customary principle of international law.

The field of international relations has approached the definition of what constitutes international law in a somewhat different manner. First, within international relations, international norms is a more commonly used phrase than international law. The concept of an international norm has been defined in a number of ways. Finnemore and Sikkink (1998, p. 891) define a norm as “a standard of appropriate behavior for actors with a given identity.” Raymond (1997) pieces together a definition that says norms can be considered “shared understandings of standards for behavior” (Klotz, 1995, p. 14); “that guide human behavior” (Jensen & Miller, 1997, p. 86); by “indicat[ing] how states should behave” (Barnett, 1995, p. 38). And March and Olsen, adopting a more sociological perspective, define norms as institutions, stating they are “a relatively stable collection of practices and rules defining appropriate behavior for specific groups of actors in specific situations” (March & Olsen, 1998, p. 948).

In addition to slightly varying definitions of norms, there have been a number of different types of norms outlined in various works. For example, some discuss regulative norms that constrain behavior, and constitutive norms that create new actors or interests or forms of action (Finnemore & Sikkink, 1998). There is also the division of international norms into hard and soft norms (Abbott & Snidal, 2001). Hard norms are more akin to the legal definition of international law and are defined as legally binding obligations that are precise and provide mechanisms or authority for implementation and interpretation (Abbott & Snidal, 2001). Soft norms, however, are more akin to the broader category of international norms and can be defined as those norms that fall short on one or more of the three requirements of hard law: precision, obligation, or delegation (Abbott & Snidal, 2001). Hard and soft laws can interact and act as complementary tools and build on each other (Pollack & Shaffer, 2013). Soft law instruments, such as UN General Assembly declarations, can generate support for creating hard laws in the form treaties or customary international legal norms (Dunoff, Ratner, & Wippman, 2010). The relationship between hard and soft law can also be antagonistic, as their interaction can create conflict and fragment the legal order. States can strategically utilize both hard and soft law to shape international law to conform to their substantive preferences, which has detrimental effects on internationalization of international law (Pollack & Shaffer, 2013). Despite the increasingly extensive and in-depth work on hard and soft law, many practicing international lawyers still question whether international law can be divided in this manner and continue to resist the term soft law (Raustiala, 2005).

Whether the term is international law or international norms, however, “at the margin norms and rules cannot be sharply distinguished from each other [and] it is difficult if not impossible to tell the difference between an ‘implicit rule’ of broad significance and a well-understood, relatively specific operating principle” (Keohane, 1984, p. 59). Therefore, the remainder of this article will use the terms international law and international norms interchangeably to indicate those rules codified at the international system level, which then may be internalized by states domestically.

Whichever definition of international law or international norms you adopt, one of the first questions the literature has addressed is how norms are created. While there have been a number of theories concerning the development and emergence of international law, one of the most widely recognized in the international relations literature is the theory of norm emergence put forward by Finnemore and Sikkink (1998). In this theory, new concepts for international norms or international law emerge through a norm entrepreneur. A norm entrepreneur is a person, group of persons, institution, or state that has strong notions about appropriate or desirable behavior in their communities (Finnemore & Sikkink, 1998). After the norm emerges and is advocated by the norm entrepreneur, it becomes more widely recognized by decision makers, until it reaches a tipping point where the norm achieves recognition. From this point, there is a cascade of recognition and acceptance of the norm into the general population. Finally, the norm becomes widely accepted and deeply ingrained enough that it is accepted as the appropriate standard of behavior (Finnemore & Sikkink, 1998). (This process is discussed in more detail in the section “The Process of Internalization.”)

While this process has been generally demonstrated to apply across states in terms of norm emergence, recognition, and general acceptance, the final part of Finnemore and Sikkink’s theory, norm internalization, has not yet been the subject of a significant amount of scholarly research. The area is ripe for study, however, as it is evident that the internalization of international law is a fundamental component of compliance and varies across states, occurring more rapidly in some states than others. There are a number of different factors that might explain the variation of internalization of international law among states. Some theories have divided these factors into institutional and cultural attributes. For example, Simmons (2009) focuses on the institutional factors of judicial review. Zartner (2014), on the other hand, considers both cultural and institutional factors as equally important for internalization. These variations in the process of internalization may, correspondingly, result in a greater role for international law in shaping the behavior of some states than others.

The Importance of Understanding Internalization

It is important to consider the internalization of international law to understand the influence of norms on state behavior. The incorporation of international law into the domestic understandings of appropriate standards of behavior and the structure of a state is necessary for these rules to act as influences on state and sub-state actors. If international law is only recognized at the global level, its influence on the behavior of these actors is likely to be minimal. Rules and norms become binding when they become part of the fabric of a society and when they are considered obligatory. Internalization of internationally drafted and ratified rules into the different domestic systems and cultures is a necessary step to achieve this (Finnemore & Sikkink, 1998; Henkin, 1979; Zartner, 2014).

Understanding how international law is internalized within a state, therefore, is a key factor in understanding the role that international law plays in shaping behavior. International law can only gain true force if states internalize the international norms that make up international law (Rosenblum, 2006). As stated by Koh (1997, p. 2659), “only once states internalize international law, do they establish internally binding domestic legal obligations.” Internalization of international law into domestic law is, therefore, linked to the body of literature on compliance with international law. Within the field of international relations, a significant amount of research has been done on state compliance with international law and under what circumstances compliance is more or less likely (Koh, 2005; Simmons, 1998). It must be recognized, however, that compliance occurs more often when states feel obligated to comply. The internalization of international law into the fabric of domestic law significantly increases the likelihood that states feel obligated to comply. This occurs for three primary reasons.

First, internalizing international law into the fabric of domestic law makes the tenets of international law punishable through domestic legal mechanisms (Zartner, 2014). It is recognized that one of the more difficult aspects of international law is that there are few concrete enforcement and punishment mechanisms at the international system level. Many international treaties do have penalties for noncompliance, and there are a number of international courts and other adjudication fora, but none of these have the same enforcement abilities as those that exist within a domestic system. Internalizing international law into domestic law makes the international legal rules part of the domestic law, and therefore violations of these rules are violations of domestic law and are then subject to the same enforcement and adjudication mechanisms as all other domestic law.

A second reason why the internalization of international law is important for increasing the likelihood of state compliance with international law is that once international law becomes part of the domestic fabric of law, the potential for reputational damage for noncompliance with these rules is increased, not only internationally but domestically as well (Zartner, 2014, p. 41). Reputation has been a key motivating factor behind state compliance with international rules (Brewster, 2013; Downs & Jones, 2002; Simmons, 1998, 2000, 2010; Zartner & Ramos, 2011). Most international relations studies have demonstrated this connection at the international system level; states want to have a good reputation among other states, so they comply with international law. But reputational concerns can matter domestically as well. Particularly in democracies, if international law has been woven into the fabric of domestic law and is considered binding, the consequences to elected leaders of violating these rules are potentially significant: much more so than if the international norms are not internalized. The internalization process increases both the sense of legal obligation and the recognition of the international legal principles as binding, as well as the costs to governments if these binding norms are not upheld (Zartner, 2014).

Finally, the internalization of international law can have an impact on a community’s understandings of acceptable behavior and create shifts in societal acceptance of what is right and what is wrong. This can have an impact on changing state laws and practices. This is particularly important in areas such as human rights or the environment where some domestic laws and practices, grounded in specific histories, contexts, and traditions, have been slow to recognize ideas about equality, rights, and justice. The internalization of international law can push understandings about these issues in new directions, which can improve protections for all. This has occurred in instances, such as with the internalization of international norms on women’s rights shifting domestic practices on female circumcision (Kwoka, 2007), indigenous rights to land as a cultural and spiritual part of their traditions (Anaya & Williams, 2001; Zartner, 2020), and even, in the United States, the idea that the juvenile death penalty is no longer in line with understandings of acceptable punishment (Roper v. Simmons, 2005)

Theoretical Approaches to Internalization

Despite the importance of internalization of international law into domestic law for understanding the true impact of international norms on the behavior of state and substate actors, study of internalization has only become a more frequent topic of research within the field of international relations since the early 2000s (Bianchi, 2004; Zartner, 2014). In the past decade, we have seen a shift as the study of international law, compliance, and norm internalization generally have become more widely considered within the field. It remains true, however, that discussion of the internalization of international law into the domestic law of a state is an issue area more widely addressed within the field of international law than in international relations. The reasons for this could be many, but some have identified the fact that investigating how international law is internalized among different states often requires extensive knowledge of domestic systems, structures, constitutions, and laws, which makes state-by-state analysis difficult for non-specialists. Among international relations scholars, the attention given to the importance of international law, and thus consideration of the mechanisms of internalization of international law, vary by theoretical approach (Rosenblum, 2006). While different strains of literature within each approach may differ slightly, the primary treatment of the main theoretical approaches in the field of international relations are discussed in the following paragraphs.

Realism, which can be divided into classical realism, neorealism, and neoclassical realism, generally pays little attention to international law, let alone factors that influence the internationalization of international norms. Classical realists such as Morgenthau and Carr recognized the existence of international law, and indeed accepted that international law had the ability to influence state behavior by providing a moral compass that underlined state action (Carr, 1946; Morgenthau, 1985). Classical realism, however, held that international law was primarily a construct of the power relationship among states and did not consider whether and how the internalization of international law might matter. Neorealism, developed in the 1970s, pays even less attention to the role of international law on state behavior and whether, how, and to what effect the internalization of international law influences such behavior. Neorealism maintains that international law is merely a tool that states use to further their own interests and power position relative to other states (Goldsmith & Posner, 2005). Since for neorealists international law has no independent binding authority, the questions over whether international law becomes internalized, how it becomes internalized, and whether this ultimately matters for shaping state behavior are not part of the neorealist research agenda. Neorealism focuses on international system-level factors and the power relations among states, and it does not consider the variations in domestic institutions and culture that may influence state responses to international law.

Neoclassical realists, however, do take domestic institutional structure into account to some extent when considering what shapes state action. While accepting the primary neorealist tenet that relative material power capabilities establish the basic parameters of a state’s actions, they recognize that the perceptions of these capabilities by decision makers, and their freedom to act, may be influenced by domestic factors (Rose, 1998). While no work has been done by neoclassical realists to date on the role that internalization of international law might play in framing perceptions that state decision makers have of their power capabilities vis-à-vis other states, this type of research is seemingly within the realm of possibility for neoclassical realism in a way that it has not been for earlier strains of the realist theoretical approach (Rose, 1998).

Neoliberal institutionalism adopts the primary assumptions of neorealism, assuming an anarchic international system in which states are rational actors concerned with their relative power position (Keohane, 1998). Neoliberal institutionalism also recognizes, however, that international institutions, which have increased greatly in number over the past several decades, influence state decisions through the reduction of transaction costs (Keohane, 1998). While not discussing international law and its internalization specifically, the recognition of transaction costs, whether reputational costs or a sense of legitimacy of state action, has the potential to implicitly consider internalization because it is internalization that creates the sense of legal obligation, which forms the foundations of concerns over reputation and legitimacy of action. No explicit study of this relationship between internalization and the effects of international institutions on state behavior has yet been conducted by neoliberal institutionalists. One limiting factor is that many neoliberal institutionalist theories, like neorealism, focus predominantly on system level factors, thereby bypassing any study of the domestic factors that may influence state behavior, such as internalization.

Liberal theory, however, focuses explicitly on domestic factors that influence decision making, and therefore is ripe for considering the influence of domestic factors on internalization of international law and how this might influence state behavior. Liberalism argues that state behavior has its origins in domestic politics (Rose, 1998). Liberal theory explicitly examines the relationship of states to the domestic and transnational social context in which they are embedded and recognizes that this relationship has an impact on state behavior in the international system (Moravcsik, 1997, 2013). Further, Trachtman (2010) argues that compliance is always dependent on contemporaneous domestic political decisions, and there is interdependence between home-state domestic politics and foreign-state domestic politics. He contends that previous social science theories of international law, such as neorealism and neoliberal institutionalism, examine state structure as an aggregate (or unitary model) and evaluate a state’s compliance under circumstances that include threat by retaliation, reduced reputation, or reduced opportunities for future cooperation. He argues, however, that by observing the unitary model of the state, social scientists fail to observe how the interests of different constituencies within a target state are advanced by compliance with international legal rules (Trachtman, 2010). While, again, no study has, up to now, examined how preferences impact the internalization of international law, or how the internalization of international law shapes the preferences of decision makers, liberal theory, because of its focus on domestic factors, has the possibility of engaging in this kind of research. As suggested throughout this article, the extent to which international law is internalized within the domestic system of individual states has a significant impact on the decisions that states make. How these preferences are shaped is a core question of the liberal theoretical approach.

Like liberal theory, constructivism allows for a potentially greater consideration of the internalization of international law than the other theoretical approaches. The process of norm internalization stems in great part from the constructivist literature, by recognizing that only through internalization into the domestic society will norms be truly binding. Moreover, constructivism allows for the consideration of the cultural and societal aspects of internalization that may shape the extent to which a state feels bound by international law. Constructivists focus on the creation of state identity, which in turn shapes state action, which then can reconfigure understandings of identity. Recognition that state identity is shaped by the cultural and institutional context within which states act and thus shape their actions, including the internalization of international law, is a cornerstone of the constructivist approach (Brunnée & Toope, 2013; Katzenstein, 1996; Zartner, 2014).

Critical theoretical approaches, such as feminism and critical race theory, would also more specifically consider culture, values, and identities as shaping factors for the understanding and interpretation of international law (Charlesworth, Chinkin, & Wright, 1991; Mutua, 2009). While not much work exists explicitly tying critical approaches to internalization, the underlying focus of these theories on addressing power imbalances, inequitable structures and institutions, and social responses are very much relevant, both to how cultural factors can impact the internalization of international law and in terms of those laws people accept as binding (Chimni, 2018). This is an area where we would benefit from additional research.

International legal scholarship views internalization in a slightly different manner than international relations theories. Given the practical importance international lawyers and legal scholars attach to law maintaining a useful nature, it is considered an essential part of the formation of new international legal rules that they be incorporated into the domestic laws of states. It is through this action that these international rules gain their obligatory status. Indeed, it has become more common for treaties to contain specific provisions that require affirmative action on the part of states, to enact domestic legislation incorporating the treaty provisions into domestic law, so that they may not only guide action, but also provide concrete remedies should their provisions not be followed. For example, the Convention against Torture and Other Cruel, Inhuman, or Degrading Treatment or Punishment, Article 3, requires that state parties enact domestic legislation prohibiting refoulement in a situation of likely torture. Another example can be seen in the Kyoto Protocol, which requires Annex I countries to implement specific reductions targets and other environmental protections within their domestic laws.

The Process of Internalization: Institutional and Cultural Influences

As mentioned briefly, many of the works that do consider the importance of internalization do so by focusing on the institutional and/or cultural factors that facilitate or hinder the process. Some consider the role of judicial institutions and their place in the process (Simmons, 2009; Zartner, 2014); others consider the overall similarities between domestic legal systems and the international law at issue (Mitchell & Powell, 2011); while still other theories move beyond the institutional factors and consider how the legal culture of a state facilitates or hinders internalization (Zartner, 2014).

Institutional Factors Affecting Internalization

Monism versus Dualism

Whether a state adopts a monist or dualist position toward international law can influence how easily international law is internalized into the domestic system. A monist state is one in which, after ratification or governmental acceptance of a principle of international law, that law automatically becomes part of the domestic law of the state and can be applied by state courts and relied on by citizens of that state (Keyuan, 2010; Zartner, 2014). No further domestic action is required to make the international law binding. While the extent of monism may vary somewhat, the following states are all generally classified as monist states: the Netherlands, Japan, Mexico, Portugal, Spain, and Switzerland. Many francophone African countries have also adopted a more Monist approach (Fombad, 2012). This does not mean that in a monist state ratification of an international treaty, for example, automatically integrates the international law into the domestic societal perceptions of law, since the norm internalization process still must occur. What it does mean, however, is that the internalization process may be facilitated by the absence of additional layers of institutional involvement before the norm has a chance to cascade into the societal consciousness. Thus, the likelihood of internalization is improved.

A dualist state, however, is one in which additional domestic action is required to make the international law part of the domestic law. Often this takes the form of legislation that incorporates the international law into the domestic legal system, but it could also require an executive decree or even a public referendum if a state’s domestic laws so require (Cassese, 2012; Zartner, 2014). One of the key hurdles that must be overcome in a dualist system is that there are additional political entities brought into the legal process, and the more players you have, the more difficult it is for the international law to become part of the domestic legal system. Examples of dualist states include Canada, the United Kingdom, Australia, Italy, and Germany. Another common form of dualist states are those with religious legal traditions, such as Saudi Arabia, where any international law must conform with the foundational religious laws of the land, which often requires review by a religious council, court, or clergy (Powell, 2020; Zartner, 2014).

Many states are not clearly monist or dualist and may retain elements of both approaches to the internalization of international law. Some argue that this is actually a third approach to internalization, one that “attempts to modify the dualist position” and suggests there is no “common field” between international and domestic law; therefore, neither is more important in the legal hierarchy than the other (Keyuan, 2010, p. 937). The two systems are rather “closely linked and infiltrate and supplement each other” (Keyuan, 2010, p. 938). The United States Constitution, for example, appears to indicate that the U.S. is a monist state by declaring that treaties are the supreme law of the land (U.S. Constitution, Article VI). In practice, however, the United States acts primarily as a dualist state. In providing advice and consent, the U.S. Senate often declares treaties nonself-executing, which means that for the provisions of the treaty to be applicable to U.S. citizens and the U.S. government domestically, legislation must be passed by Congress implementing the provisions of the treaty into U.S. domestic law. Generally, only once this occurs may the provisions of the international treaty be relied on in a suit before domestic U.S. courts. This contributes to the delay in internalization of international legal principles, which occurs often in the United States. A similar process occurs in Canada, where international customary norms are held to be automatically internalized under historical provisions of the common law, but where international treaty provisions must be “transformed into the domestic legal order through implementing legislation or another domestic law-making process” (LeBel & Gonsalves, 2006, p. 4).

In the countries of the European Union (EU), the role that monism and dualism play in the internalization of international law provides a different perspective. Individual member states of the EU each have monist or dualist positions ingrained in their domestic legal structures. For example, France, the Netherlands, and Spain all lean toward monism; Italy, Germany, and the Republic of Ireland are dualist. Upon joining the European Union, however, each member state agrees to essentially act as a monist state in relation to European Union law. Particularly in the case of EU regulations, EU law is held to be immediately applicable in member states without further action of the part of domestic legislatures. Moreover, because the European Union has begun to legislate at the regional level on a number of subjects that are traditional topics of international treaties—such as human rights and the environment—this has allowed even dualist states that are members of the EU to more easily internalize certain international legal provisions into their domestic systems.

Among countries in Africa, there has been a trend post-colonialism, and with renewed vigor in the 1990s, of internalizing international law to assist with constitutional development and interpretation (Fombad, 2012). In many of these countries, internalization “can be understood as the development of the adoption in national constitutional laws of many shared norms whose origins can be traced to international and regional supra-national laws” (Fombad, 2012, p. 444). This has led to internalization of international legal principles, such as the precautionary principle, but also enhanced support for principles of democracy and human rights, which may be able to draw on international law through internalization, even, in some instances, in the absence of domestic protections.

Legal System and Institutional Design

While significant in the internalization process of international law, whether a state maintains a monist or dualist system is not the only factor that determines the ease with which international law is internalized. Monism or dualism works in conjunction with other institutional and cultural factors within each state. For example, most dictatorships may be viewed as monist because an authoritarian leader’s accession to a treaty is usually enough to indicate the state is bound by that treaty. The monarchical structure of Saudi Arabia’s legal system allows for some elements for monism because the king’s supreme authority provides him the responsibility for ratifying international treaties (Zartner, 2014). However, the additional step of ensuring that international law conforms with the Shari’a law in Saudi Arabia actually makes the state dualist. Still, many long-standing democracies, like Canada and Australia, are dualist, but have relatively strong records on international law compliance, despite the hurdles of internalization. Regime type, therefore, in addition to monism or dualism, influences internalization of international law.

Regime type has the potential to play a role in the facilitation or hindrance of the internalization of international law into the domestic law of a state. The example introduced in the previous paragraph shows how a dictatorship or authoritarian state may be considered monist in nature and may not have many domestic constituencies that need to accept international legal provisions; however, given the nature of an authoritarian regime, this does not necessarily mean that the principle of international law has actually been internalized. In this vein, regime type is a key component to understanding the role of law in interstate relations (Simmons, 1999). While this may have something to do with the concentration of power in a dictatorship versus a democracy, it more likely is a response to shared values and comfort with international law. Those regimes that are based on the rule of law, that uphold values supporting human rights or peaceful resolution of disputes, and that prefer cooperation to conflict to solve disputes are more likely to recognize international law as valid and will more easily internalize its principles than those states not grounded on these characteristics (Simmons, 1999).

A number of other institutional characteristics affect the internalization of international law, including the separation of powers and the role of the courts within the domestic system (Mitchell & Powell, 2011; Simmons, 2009; Zartner, 2014). This examination of the different institutions and legal systems within a state that may influence internalization can draw significantly on the comparative law literature, which, while not addressing the question of internalization specifically, does consider the differences in domestic legal institutions and how this results in different perspectives on international law generally (Mitchell & Powell, 2007, 2011; Zartner Falstrom, 2006). The relationship between branches of government, the regime type of a state government, and the role and strength of the judiciary in creating and implementing law can all have a significant impact on the process of internalizing international law into the domestic legal system, and in turn, on the extent to which states comply with international law (Fombad, 2012; Zartner, 2014).

The separation of powers within a state can have an impact on internalization in much the same way that a monist or dualist approach may have an impact. The greater the number of actors that must be involved in the internalization of international law within a state, the less likely it is that the law will be successfully internalized to the point of becoming a legal obligation that shapes state and nonstate action (Tsebelis, 2002; Zartner, 2014). For example, in the United States, where internalization of international treaties provisions requires action on the part of at least two branches of government (the executive branch and the legislative branch), the process is significantly more political and takes longer than in states where any internalizing action is solely within the purview of one branch of government (Diehl, Ku, & Zamora, 2003). Therefore, even if state leaders accept an international legal principle at the international system level, convincing domestic constituencies that this law is valid and should be incorporated into domestic law may prove difficult. The larger the number of domestic constituencies that must be convinced to internalize the international law, the more unlikely it is that such internalization will occur (Diehl et al., 2003).

Overall institutional similarity between domestic and international law may also play a role in facilitating or hindering internalization of international law into domestic law. Research has shown that those states where there is institutional similarity between the structures of domestic law and the structures of international law are more likely to accept international law as valid and binding (Mitchell & Powell, 2007, 2011; Zartner, 2014; Zartner Falstrom, 2006). In states where the judicial branch has substantive power to make and interpret law, the internalization of international law may be hindered because the judiciary at the international level is not responsible for law making, only law application (Bianchi, 2004; Simmons, 2009). For example, states like the United States, which follow the concept of precedent or stare decisis, may have greater difficulty internalizing international law than states that do not adhere to this concept, because international law does recognize the principle of precedent (Mitchell & Powell, 2007, 2011; Simmons, 2009; Zartner, 2014).

Norm Internalization Processes and Legitimacy

In addition to the institutional structure affecting the internalization of international law, the process by which norms are internalized has a significant effect. Perhaps the leading theory on the norm emergence and internalization process is that put forth by Finnemore and Sikkink, in which they describe a three-step process of norm emergence, norm acceptance, and norm cascade (1998, p. 895). Normative concepts are introduced by norm entrepreneurs who attempt to convince a critical mass of states or individuals to embrace the new norms as binding (1998, p. 895). Eventually, when there is a critical mass persuaded by the norm entrepreneur to embrace the emerging norm, a tipping point is reached as more and more states or individuals accept the norm. States may accept a new norm for a number of reasons, including pressure for conformity, desire to enhance international legitimation, and the desire of state leaders to enhance their self-esteem (1998, p. 895). This then leads to a norm cascade facilitating norm internalization within a state or community where the norm acquires an obligatory quality, becoming part of the social fabric.

Finnemore and Sikkink recognize, however, that this process may vary among states as it can be influenced by different social processes, as well as different actors, motives, and mechanisms of influence such as those institutional and cultural factors described here (1998, pp. 894–895). Internalized norms then become the prevailing standard of appropriateness for behavior against which new norms then emerge. A similar norm internalization process has been put forward by Koh (1998), confirming Goodman and Jinks’s (2003) theory that social mechanisms are crucial for understanding norm internalization, including the internalization of international law into domestic law.

Cultural Factors Affecting Internalization

The institutional design of a state is not the only factor to consider when examining how international law is internalized within a state. A number of international law scholars have recognized the interconnectivity of domestic legal culture and behavior of states toward international law (Charney, 1997; Jouannet, 2006; Koch, 2003; Powell, 2020; Powell & Wiegand, 2010). Internalization can only occur with local legitimation and support. Local legal systems, however, are vastly different from one another in terms of the legal culture they adhere to and the beliefs in the role of law for society that they accept. This means that internalization will take on different forms and require different processes in different states.

Attitudes About Law and Appropriate Standards of Behavior

Certain cultural attributes are more accepting of outside influence than others and thus are more likely to easily internalize international law into the domestic law. Western legal traditions—common law and civil law traditions, for example—have more in common with international law and its focus on secular creation and written rules, and they share similar ideas about rights and freedoms. Therefore, many Western states are more likely to accept and incorporate international law into their domestic legal systems. This is because understanding international legal rules is easier when the format, substance, and ideas behind the international rules closely mimic the state’s own domestic law.

However, other legal traditions have very different conceptions of law—how law should be created, and the role of law in society—that do not so closely mimic today’s international legal rules. This can make internalization of international law more difficult. For example, states whose legal traditions are founded on religious legal traditions often have very different societal understandings of law and do not accept external law created by nonreligious authorities that may contradict their religious beliefs. In these circumstances, it can be difficult to internalize international law until a way is found for the international legal rules to be in conformance with the domestic religious legal tradition. This has been an ongoing issue, for example, with states in which the legal system is based on Shari'a law. Many of the provisions of some of the international treaties on women’s rights, for example, are seen as being contrary to some state's interpretations of Islamic teachings. This greatly hinders internalization of those treaty provisions even should the state ratify the treaty. This issue is not limited to religious systems, however. States within the East Asian legal tradition are often reluctant to internalize international law, not necessarily because it conflicts with any specific principle of domestic law, but because written law generally has a very different place —a less important place—in society than it does in many Western legal traditions (Powell, 2020; Zartner, 2014).

Nonstate Actors and Public Opinion

Another component that may affect the ease with which international law is internalized into the domestic law of the state is the role that nongovernmental organizations (NGOs) and interest groups may play in the internalization process (Charnovitz, 2006). Despite the immense presence of nonstate actors in international life, international legal scholarship has often minimized the role of nonstate actors and NGOs until recently (Spiro, 2013). The level of involvement of nonstate actors also varies across states, being affected by regime type, domestic law, and societal support for the activities of NGOs and the impacts of social movements. It has been found, though, that the incorporation of international norms into the domestic fabric of a state may be greatly facilitated when there are nonstate actors on the ground promoting such internalization and creating positive public opinion toward international law and legal issues (Kwoka, 2007; Risse, Ropp, & Sikkink, 1999). If domestic interest groups, NGOs, or other nonstate actors are opposed to a particular international norm because they feel it is contrary to their interests or their values, their active opposition to such internalization can significantly reduce the likelihood the international law will successfully be internalized (Diehl et al., 2003). For example, “labor and manufacturing groups in the United States have sought to weaken the adoption of domestic regulatory mechanisms that give effect to international environmental agreements” (Diehl et al., 2003, p. 61). Therefore, in those states where there is active NGO participation in the norm emergence and internalization process, the domestic internalization process is greatly facilitated when NGOs support the international legal principles the state has accepted.

Analysis and Direction for Future Research

As this brief discussion of the internalization of international law indicates, there are a wide variety of factors that can facilitate or hinder the internalization of international law into domestic law. While a number of important works have come out in the past five years that consider internalization (Mitchell & Powell, 2011; Simmons, 2009; Zartner, 2014), there is significant opportunity for additional research on the topic of the internalization of international law into domestic law. Given the importance of this subject for our overall understanding of the power of international law to shape the behavior of state and nonstate actors, continuing to develop work in this area is important.

Which Norms Will Be Internalized?

As in the case with the compliance literature, one of the key questions that needs more thorough examination is which norms will be internalized. As indicated, widespread agreement among international lawyers and international relations scholars is that internalization is a key component of solidifying the obligatory nature of international law and ensuring compliance. However, despite Louis Henkin’s (1979) oft-repeated statement, that most states comply with most international law most of the time, some recent empirical studies have questioned whether this is true for all norms. One of the most prominent is by international legal scholar Oona Hathaway (2002), whose empirical study of compliance with international human rights agreements found that compliance may actually decrease with treaty ratification. What Hathaway does not address is whether, upon ratification, the states in her study had internalized the international law at issue or not. Moreover, she does not consider whether some norms are internalized, and thus complied with, more frequently and extensively than others.

As described, there are different kinds of international law. Whether you prefer the legalistic divisions between treaties, custom, etc., found in the Statute of the International Court of Justice or the hard and soft law division, there are clearly different kinds of international law. One question that remains to be addressed is whether the form of the international legal principle at issue matters. For example, are treaties more likely to be internalized than customary principles? Moreover, it is important to consider the subject matter of the international law. Are some legal rules more likely to be internalized because they cover international environmental law as opposed to other rules on international human rights law, which are very difficult to internalize? A study across different types of norms may help us identify if there are certain areas where states consistently have difficulty internalizing, and thus complying with, certain types of international law.

Institutional and Normative Factors Influencing Internalization

In considering which norms will be internalized, it is important to consider the institutional aspects of internalization as well as the cultural characteristics of each state that may or may not facilitate internalization. While it has long been recognized that different states will deal with international law differently (Henkin, 1979), a number of scholars have recently explored the effect of different institutional mechanisms or legal systems on internalization (Mitchell & Powell, 2007; Powell & Wiegand, 2010; Zartner Falstrom, 2006). Studies that delve into more detail about which institutional and normative characteristics may contribute to or hinder internalization could contribute a great deal to our understanding of internalization. For example, how much does religion play a role in the internalization process? In states with a legal tradition founded on religious law, are we more or less likely to see internalization of international legal principles? How about societies with tightly held constitutional principles, such as in the United States—can that affect the internalization process? These are all questions that remain to be addressed.

It is also important to acknowledge that there is a question of the applicability of international law, and therefore internalization, to communities in the Global South (Chimni, 2018; Rajagopal, 2012). There are communities and scholars around the world who are concerned with structural inequalities in the creation, acceptance, interpretation, and enforcement of international law as a Western hegemonic endeavor. For these communities, the question of international law and the appropriateness of its internalization into their countries’ domestic law, in and of itself, is still a question to be addressed.

The Politics of Internalization

Even as our understanding of the importance of internalization has grown, tensions are evident in some circumstances where the internalization of international norms is either ignored by those in power or viewed with hostility by certain groups within a society. One of the more pressing questions that has developed when thinking about the role and power of international law in the year 2020 is how do we contend with the rise in nationalism and increasing isolation among states, both in terms of foreign policies, but also in cultural movements within states that are impacting elections and fomenting xenophobia, racism, and anti-globalism in some cases (Woo, 2018).

While resistance to international law is growing among some groups, it is also true that international law can be a powerful tool for advocacy groups and activists at the grassroots, as well as state and regional levels, especially when there is a judiciary or other sub-state actor willing to draw on internalized law in opposition to executive reluctance to accept.

For example, international norms regarding climate change have been internalized by publics around the world, including in countries like the United States and Australia, yet the national governments in these countries refuse to accept these new standards. This is creating tension between the population and the government. In some cases, however, like the United States, since 2017, the state and lower federal courts have stepped in to address environmental issues, often solidifying protections when the executive branch and other government agencies will not. Similar patterns can be seen regarding immigration law, where lower U.S. courts have consistently struck down parts of the executive’s efforts to restrict certain migrants.

Cases and courts relying on international law is one of the foremost ways in which we can see the impacts of internalization. In a recent Colombia Supreme Court decision, the Court held that the government had a responsibility to protect intergenerational equity through better protections of the environment, including protecting the rights of the Amazon. In rendering its decision, the Court relied on international and regional norms, like those of the Inter-American Court of Human Rights to support the logic behind its decision. Similarly, in the recent Urgenda case in the Netherlands, the courts referred to regional and international law to support the ruling that the government failed to protect the rights of its citizens in not doing enough to address climate change.

The body of international law continues to grow. Therefore, the question of how this international law is interpreted, utilized, relied on, and complied with will continue to be of great importance. Since internalization of international law is, ultimately, a domestic action, the role of domestic politics is likely a key factor in every stage of the internalization process. For example, consideration of the difference between democracies and authoritarian governments has generally held that democracies are more likely to internalize international legal norms largely due to shared values between democratic legal principles and international law. However, questions remain as to whether this holds true for all international law, or whether we are more likely to see this pattern emerge for certain types of legal principles—such as human rights laws—and whether we are more likely to see internalization occur for bilateral treaties over multilateral treaties or customary forms of international law. Moreover, considerations such as the role of domestic politics, interest groups, civil society, and even local judiciaries on the internalization of international law into the domestic systems of a state have not been made in a rigorous manner. Assessment of veto players, political party control, and power and interests could all be studied in terms of their influence on the internalization of international law in to the domestic legal system.


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