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date: 20 August 2017

Theories of Interstate Peace

Summary and Keywords

Few theoretical formulations are specifically devoted to accounting for peace, as opposed to war. Nevertheless, the occurrence of peace requires a different explanation than that for war. There are multiple conceptual definitions of peace, and to a significant extent these lead to different theoretical explanations. Peace, except for its “negative peace” variant, fits poorly into various “grand” international relations theories such as realism, liberalism, and constructivism. Nevertheless, there is a relatively small, but emerging, middle-level set of theoretical works that directly addresses the transformation of hostile relations to peaceful ones, in both negative and positive varieties.

Keywords: peace, war, positive peace, negative peace, cooperation, security communities, Kantian triad, realism, liberalism, constructivism, empirical international relations theory


Most theoretical approaches begin with accounting for violent conflict between actors, notably at the highest level of such conflict—war. In contrast, few begin with peace or understanding cooperative relations. Geoffrey Blainey’s book (1973, p. 293) claimed, “War and peace appear to share the same framework of causes … The same set of factors should appear in explanations of the outbreak of war [and the] outbreak of peace.” If this is true, then there is no need for a separate theory of interstate peace; one could merely take theories of war and look at the reverse or absence of the factors causing violence and have an explanation for peace. Nevertheless, peace is far from symmetrical (Goertz & Mahoney, 2012) to war. Accordingly, an understanding of peace requires theories distinct from those that seek to explain war.

Peace is distinguished from war in a number of ways. First, peace and war are different phenomena; war can be seen as a distinct event or series of related events. These are confined to a defined, sometimes brief, time frame and location. By definition, a war involves primarily military interactions. In contrast, peace is a relationship that involves many different kinds of interactions; many are diffuse and involve different actors. Peaceful relationships often evolve in long-term processes, thereby beginning and ending in steps or phases rather than abruptly.

The occurrence of peace is empirically distinct from war and militarized confrontations. The incidence of the highest levels of peace is only weakly correlated with interstate war (Diehl, 2016), not perfectly so as would be the case if the two were symmetrical, and indeed at the system level, peace is slightly positively related to interstate rivalry (Goertz, Diehl, & Balas, 2016), the most contentious of relationships.

The causal factors that account for peace are often different, and are certainly not mirror images for those explaining war. For example, how powerful states are vis-à-vis each other is a critical component in most studies of war. The capability distribution between states is a central part of realist thought as well as some postmodern treatments that emphasize exploitation and inequality. When the focus shifts to peace relationships, however, it is not clear that either equal or unequal capabilities should be associated with the development, much less the most advanced forms of peace.

Thus, if peace is different than war, it requires a different theoretical formulation. Accordingly, we review the theoretical work on peace. The focus of this article is confined almost exclusively to peace in the context of state-state relations or the interstate system writ large. The scholarly work on this topic is more developed than on “internal peace,” and in any case these two forms of peace are built from fundamentally theoretical and empirical bases. We begin with the different conceptual definitions of interstate peace. There is not as clear a consensus on these definitional aspects as there is for war, and to a significant extent different conceptions lead to different theoretical explanations. We then discuss how peace fits into various “grand” international relations theories such as realism and liberalism. Finally, we examine the relatively small, but emerging, middle-level theoretical work that directly addresses peace.

Conceptual Elements of Peace

Regan (2014) traces some of the origins of scholarly conceptions of peace to the work of Wright (1954) and Cottrell (1954). There, the distinction was made between what we would now refer to as “negative peace” and “positive peace”. This differentiation, and in particular an illumination of the latter, would later become identified with the classic work of Galtung (1971).

Negative peace is the concept on which there is most agreement, defined by the absence of war or large-scale violence. This is reflected in most international relations scholarship, including some prominent works that tout the emergence of a more peaceful world (Goldstein, 2011; Pinker, 2011). Similarly, an extensive scholarly literature explores the “democratic peace” (Russett & Oneal, 2001). This depends entirely on the absence of a bona fide war between two democracies, not the absence of armed conflict or highly militarized interactions per se. Similarly, the period called the “Long Peace” (Gaddis, 1987) after World War II, is defined as the longest period of history without a war between major power states. In these approaches, scholars typically examine patterns in warfare and explanations for the outbreak for war. If there is a decline in war or if the forces leading to violence are absent or weak, then (more) peace is said to be the result. The focus on negative peace is predominant in international relations scholarship (Diehl, 2016), even in journals such as the Journal of Peace Research and Journal of Conflict Resolution that purport to study peace and not merely war (Gleditsch, Nordkavelle, & Strand, 2014).

Negative peace comes with many different lexicons. These include “precarious peace,” (George, 2000), “adversarial peace,” (Bengtsson, 2000), “pre-peace” (Bayer, 2010), “conditional peace” (George, 2000), and “cold peace” (Miller, 2001). These focus on the high threshold event of war, while at the same time each allows some significant measure of hostility between those that are purportedly at peace. Newer formulations expand this to include cyberwarfare (Hampson, 2017) and sexualized violence (Enloe, 2017).

The concept of positive peace is more contested and indeed amorphous in many formulations. Positive peace usually includes some normative value that is maximized or a negative condition that is eliminated from interactions. For Galtung (1971), it is the removal of structural violence from a relationship and thus human rights violations and poverty do not occur; this is akin to negative peace in terms of defining something as its inverse, but here more than war is lacking. This shares some similarities with some critical theory formulations that also incorporate concerns with gender, resistance, and the environment (Richmond, 2017).

Kant’s (1795) “perpetual peace” provides for the elimination of standing armies, noninterference in the affairs of other states, and avoidance of concerns that might prompt war or violence between states. It fits within the positive peace tradition for its emphasis on republican forms of government in each state and the rule of international law governing their relations.

Lederach (n.d.) defines the concept of “justpeace” as “(1) an adaptive process-structure of human relationships characterized by high justice and low violence, (2) an infrastructure of organization or governance that responds to human conflict through nonviolent means as first and last resorts, and (3) a view of systems as responsive to the permanency and interdependence of relationships and change.” The second point is echoed by Chenoweth (2017) and Crocker (2017), who indicate that conflict between actors can be expected (even inevitable), but it is how that conflict is managed that matters; peaceful societies and interactions manage or resolve conflicts through nonviolent means. Wallensteen’s (2015, p. 3) “quality peace” requires that peace “also meet standards of dignity, security, and predictability.” Melander (2017) specifically includes gender equality as a defining feature of peace.

With justice and human dignity additions to the concept of peace, both Lederach and Wallensteen essentially focus on domestic peace, notably in post-civil war settings. In that setting, the treatment of minorities and the population in general by the state is critical. It is less clear how justice and human dignity are critical for theories of international peace.

Theoretical formulations should flow directly from the positive peace concepts, but these can be dramatically different from one another depending on the components included in the definition. Accounting for the elimination of poverty produces theories that are quite different than those associated with effective conflict management and limiting violence (Boulding, 1978). The complexity and differences increase when one adds elements of justice, gender equality, and human rights to the concept of peace.

More recently, there has a movement to consider peace in general as a continuum (Davenport, Melander, & Regan, 2017); that is, peace is not merely absent or present, but exists in degree overall or along several dimensions. This is consistent with other concepts in international relations such a democracy or national power in which actors vary in degree not kind. A theoretical construct of peace as a continuum provides a segue to the measurement of the concept empirically.

Many of the efforts to conceptualize and measure peace, even along a given continuum, suffer from two limitations for our purposes. First, they look at peace from a monadic level of analysis; that is, peace is considered from the perspective of a single country. This might be adequate if one is interested solely in internal peace, understanding subnational processes or conditions within states (see Melander, 2017; Regan, 2017). It is problematic, however, when trying to understand the relationship between that state and other countries. States have varying degrees of peacefulness vis-à-vis other actors. For example, Israel enjoys very peaceful relations with the United States, less so with European Union members, and not at all with some of its neighbors. Second, a number of the peace conceptions and associated indices essentially rely almost exclusively on negative peace, in spite of many indicators. For example, in the Global Peace Index,1 virtually every one of the 27 indicators of internal and external peace used to build the aggregate index deal with violence in some form; these include the homicide rate, access to small arms, military expenditures, and involvement in external conflicts. Hence peace is implicitly the absence of various forms of violence.

International relations theory requires at least dyadic and perhaps systemic formulations for peace and must include components that go beyond those associated with violence, militarization, and conflict—although these might be part of the conceptual and empirical equations (for a review of some possibilities, see Davenport, Melander, & Regan, 2017).

Goertz and colleagues (2016) create a “peace scale” of five ideal type categories along which state relationships vary. The scale is a holistic approach to classifying how country governments (as opposed to private actors) interact with one another. Although a wide range of considerations go into how particular pairs of states are classified, the authors identify six important considerations for comparison purposes: (1) the presence or absence of war plans; (2) the frequency and severity of conflict, especially militarized; (3) the salience of issues in dispute and whether they are mitigated or resolved; (4) the existence and institutionalization of communication channels; (5) the state of diplomatic relations and coordination; and (6) the degree to which interstate cooperation between the pair exist and are institutionalized.

Two categories of rivalry (severe and lesser) are somewhat conventional in that they are characterized by militarized conflicts and threats; accordingly, they are on the hostile side of the peace continuum and useful more as a contrast to peace relationships, although there might be peaceful elements present. Negative peace in their conception goes beyond the simple criterion of the absence of war; states are neither close friends nor enemies with one another. A wide range of relationships are found in this category from former rivals to those states that have a number of disagreements but some positive interactions as well.

The peaceful side of the continuum sets a high bar for states to be considered at positive peace. Hallmark dimensions of “positive” peace are expectations and mechanisms for peaceful conflict resolution; war or the use of military force as a means of conflict resolution is “unthinkable,” or has zero probability. Although peace scholars differ on some of the dimensions, four, related, core characteristics define the extreme end of positive peace: (1) absence of major territorial claims, (2) institutions for conflict management, (3) high levels of functional interdependence, and (4) satisfaction with the status quo. Two categories of relationships on the positive peace side of the scale are “warm peace” and “security communities.” Security communities, a term that first became prominent with the work of Deutsch, Burrell, and Kann (1957), has also received more recent attention from others (see the collection by Adler & Barnett, 1998a). Although conceptually this could include a formal merger of two political entities, in practice states retain their sovereign independence to a substantial degree. War is not only unthinkable between members, but also the parties are tied together by extensive communication links and transaction flows (Deutsch et al., 1957). Security communities might also involve shared identities, values, and meanings as well as interactions at several levels (e.g., private as well as governmental) and common long-term interests (Adler & Barnett, 1998b). The relationships are mutually rewarding and reflective of harmonious interests (Alker, 1977). Warm peace states are different from security communities more in degree than kind, with less integration and harmonization of policies.

An attempt to develop a peace concept that is broadly applicable for states, groups, individuals, and other actors is the Davenport Peace Scale (Davenport, 2017). His seven-point scale also incorporates categories describing the full range of relationships, not merely peaceful ones. The seven categories include three hostile sides of the scale (“Opposition,” “Overt Aggression,” and “Latent Aggression” respectively) and three on the peaceful side (“Latent Cooperation,” “Overt Cooperation,” and “Mutuality” respectfully. Hostile and peaceful relationships are separated on the scale by the middle category of “Indifference.” Four dimensions determine the placement of relationships in the seven categories: behavior, organization, language, and values. For example, the highest form of peace—Mutuality—involves integrating and consistent behaviors, inclusive organizations, language that refers to shared identities and common missions, and shared and positive values of community.

Conceptualizing peace as a multi-level continuum determined by multiple criteria has a number of theoretical advantages. First, it provides a more nuanced way of considering relationships than dichotomous distinctions (war/peace) that lump dissimilar interaction patterns together. Second, it moves beyond the presence or absence of war criterion to reflect better that peace is far more than avoiding the highest level of violence. Finally, a continuum encourages theoretical formulations and empirical investigations that concern the dynamics of states moving from hostility to peace (and vice versa) rather than descriptive determinations of whether peace is present or not.

Peace and Extant Grand Theory

Existing international relations theory has been primarily focused on war rather than peace. Accordingly, it has concentrated on conventional definitions of negative peace and how state actors avoid war rather than the processes associated with positive peace per se. Nevertheless, there are some variations on how peace is treated among the major theoretical traditions in the discipline (for a review, see Richmond, 2008).


Realism is almost exclusively concerned with negative peace, and even then there has a cautionary view of its stability (see Morgenthau, 1948). Classical realism assumes a state of anarchy in the world, and therefore little or no role for international norms or organizations as the promoters of cooperation found in other theoretical formulations. At best, an international system of self-help might produce some cooperative arrangements, such as arms control agreements (Glaser, 1994), but these tend to reinforce negative peace rather than promote deeper forms of cooperation such as integration. In anarchy, war is always possible, and even relatively probable. Negative peace is maintained by strong militaries and balance of power policies. As such, positive peace is not possible for realists.

If war is thought to be inevitable, then negative peace is fleeting and preparations for war are essential. Such conditions do not facilitate positive peace. Negative peace might be established by victory of one side or state in a war. This “victor’s peace” (Richmond, 2008) is not necessarily one that reflects the values of justice, equity, or other components of the positive peace variety; it is a reflection of the self-interest of the hegemon. Negative peace is maintained by deterrence and alliances through the logic underlying balance of power. Cooperation such as alliances can be temporary and shifting friendships might be needed to maintain the balance. Neorealist or structuralist approaches often include a theory of change, but it is one that refers to shifts concerning which states are the most powerful or how power is configured in the system (e.g., bi versus multipolarity); such changes from war or shifts in national capabilities do not fundamentally alter the core dynamics of power and the context of anarchy.

In sum, realism offers few insights into peace that go beyond the “not war” orientation. Furthermore, its pessimistic view of human nature and international anarchy imply that positive peace is unattainable.


There are several varieties of liberal theory that address peace and in different ways. All share the likelihood, even expectation, that cooperation is possible. Thus, unlike realism, negative peace might be expected to be more common and positive peace is conceivable under certain conditions.

Classical actor-centered liberal formulations (Bueno de Mesquita & Lalman, 1992; Moravcsik, 1997) retain the rationalist assumptions of realism, but the analytical shift is to the interests of domestic political actors to understand outcomes. The focus is still on negative peace in these constructions, but there is room for understanding greater cooperation and potentially positive peace as well. When powerful domestic political and economic interests see avoiding war as beneficial, then negative peace is more likely. If those same interests regard greater cooperation and integration as desirable, then states can move beyond not fighting to harmonize various policies, coordinate actions, and even integrate different segments of their economies (e.g., common currency).

Neoliberal theoretical formulations (Keohane, 1984) place a greater role on institutions to solve the collective action problems that stand in the way of greater cooperation. The alternative is self-enforcing agreements (often based on pure self-interest) that ensure that actors don’t free-ride or otherwise exploit one another such that cooperation breaks down. From the perspective of peace, liberal formulations require some symmetry in the preferences of two or more actors before peace and cooperation occur.

Perhaps the most prominent variant of liberal theory and one most concerned with war and peace issues is the so-called democratic peace theory, most notably based on the “Kantian triad” (Kant, 1795; Russett & Oneal, 2001). In this conception, democratic states are argued to be more peaceful than other states. Democratic states are more peaceful only toward one another, not necessarily toward non-democracies and the effect doesn’t necessarily apply to covert actions. The Kantian variation adds interdependence through trade and membership in international organizations (IOs) as the necessary legs that promote peace. Trade and IOs are the facilitating conditions and not necessarily the consequences of more peaceful relationships (e.g., the problem of endogeneity). In all cases, however, democratic peace arguments refer to negative peace; that is, democracies don’t go to war with one another and that is reinforced by trade and common IGO memberships.

The democratic peace theory and the Kantian triad are backed by strong empirical evidence, at least with respect to negative peace. Nevertheless, they are challenged by alternative explanations—the “territorial peace” (Gibler, 2012) and the “capitalist peace” (Schneider & Gleditsch, 2010)—that purport to account for the absence of war between democracies by reference to other factors. Again, these concentrate on the absence of war rather than more positive conceptions of peace. There is a theory of change embedded in the democratic peace theory, namely, that a global shift to more democratic states should produce more peaceful, or at least less militarized, relations in the long run. Nevertheless, the transformation could produce more violence in the short run as conflict prone pairs of states (democratic-authoritarian) would initially increase until a tipping point was reached and norms of peaceful conflict management spread (Mitchell, 2002).

There are a number of limitations to liberalist theories with respect to peace. First, to the extent that they are successful, they are better at accounting for cooperation rather peace per se. These are not synonymous. States that are hostile to one another or those at negative peace can still cooperate on a wide range of activities, but disagree substantially on a range of issues including territory, political order, and human rights. Positive peace entails a deeper level of cooperation and agreement on values and processes for dispute resolution across the board. Second, liberal theory is largely silent on the sources of preferences that promote cooperation, and therefore lack a specification for how transformations from war and rivalry to peace occur. Finally, liberalism has difficulty in explaining failures to cooperate or more deeply integrate when the proper domestic preferences and institutions exist. The existence of positive peace is largely a post-World War II phenomena and constitutes a relatively small, albeit growing, minority of state relationships (Goertz et al., 2016)—likely far fewer than liberal theory would predict.

In general, liberal approaches suffer from the same myopia as realist ones in focusing on negative peace. They are, however, open to the possibility of cooperation, even potentially deep cooperation although the causal process for how this occurs is often opaque.


In contrast to realism, constructivist theories do not assume that actors are inherently conflictual. Nor is there a rationalist assumption (as is true of some liberal variants as well). Rather, state relationships can evolve into ones of friendship or enemies (Wendt, 1992). In this way, the possibility of positive peace relationships is acknowledged. Rules and norms that emphasize peaceful interactions and discourse would be the key to promoting peace, or at least stabilizing negative peace.

As with other theoretical frameworks, there are multiple variants of constructivism, but they do share the assumption that reality is constructed by actors and that the resultant decisions made by that construction further shapes the interpretation of reality. Embedded in constructivism is the recognition of change, and therefore the possibility that positive peace could emerge. Attitudes and norms can evolve over time in more peaceful (or not) directions. Institutions not only reflect this but also can promote change through learning and reinforcement. Cognitive change comes from a series of processes (Dougherty & Pfaltzgraff, 2001). These first include “innovation” in which new values and ideas are accepted, followed by “selection,” which indicates the degree to which such values and ideas become embedded in the common discourse. Third is “diffusion,” in which ideas are spread from some actors (e.g., states) to a wider set of actors.

This raises the question about how such rules and norms come about in constructivist logic. Why might peaceful notions prevail over values that emphasize conflict? Take for example the seminal work of Wendt (1999), which adopts a structural view. In his conception, an anarchic international system can produce different cultures, each with their own logic and implications for peace. The Hobbesian culture has at its centerpiece the presence of enmity between self and other. Enemies don’t recognize the right of others to exist and view violence as a legitimate means to achieve ends. This leads to endemic and perpetual war, “kill or be killed.” There is not much room for peace in this environment, except perhaps negative peace achieved through states balancing one another, but this is believed to be difficult to sustain. This is a logic said to be present for much of international relations history.

A second culture, the Lockean one, is based on rivalry rather than enmity. The distinction rides on the recognition of legitimate existence of the other and thus conquest and related behaviors are not acceptable. Violence, however, is still a tool of states. War is accepted and legitimate, but not as a means to destroy states, but is limited to pursuing material interests. Respect for sovereignty, in which the weak are somewhat protected from predatory behavior of the strong, and acceptance of non-alignment make war less common and negative peace relatively stable. Again, the logic underlying rivalry, however, does not open much space for positive peace interactions.

The Kantian culture is the third variant, and is based on friendship. As Wendt (1999) acknowledges, this is undertheorized in international relations scholarship. In this culture, the main norms are peaceful resolutions of dispute (anti-violence) and mutual aid in the event of third-party threat. The structures and underlying norms are consistent with the concept of pluralistic security communities (Deutsch et al., 1957) in that one’s own security is considered synonymous with that of other actors. Still, the focus is primarily on traditional security matters even as war is “unthinkable.” Other aspects of positive peace, including economic integration, human rights, and justice, are not part of this approach.

For Wendt (1999), the master variables are interdependence, common fate, homogeneity, and self-restraint respectively in promoting Kantian culture. He notes that these have been discussed somewhat in the context of functionalism and neofunctionalism (to be discussed) but not in terms of collective identity formation. The first three factors are active causes of collective identity formation, whereas self-restraint is an enabling or permissive cause (p. 343). Only one of the three active causes is needed for collective self-identity, but self-restraint is a necessary condition for the process as a whole. Interdependence is when outcomes depend on the choices of others, and has received extensive attention in liberalism. Common fate is a related condition in that individual state well-being and survival is tied to what happens to others. Homogeneity is the degree to which states are alike institutionally and otherwise, most notably with respect to regime type as specified in the democratic peace. Self-restraint—that states won’t try to attack or conquer one another and the belief therein—is essential to overcoming obstacles to identity formation and cooperation.

Emphasis on democracy and security communities suggest that particular identities are conducive to international peace. These involve democracy and the creation of a common community of peace. Social constructivists can view democracy as an identity variable, which is consistent with a normative view of the democratic peace.

The previous perspective has at least two limitations. First, it is not clear how the desired thresholds of these variables are achieved or when some conditions are more likely than others or in what combination if more than one is present. Second, there is the question whether the specified variables are better as descriptors or outcomes of peaceful relationships as opposed to purported causes.

Other Theoretical Frameworks

The three major theoretical frameworks are strongly focused on negative peace and generally do not provide specific explanations for more positive forms of peace to the extent that they are addressed at all. A variety of other theoretical approaches do address positive peace concerns, but don’t necessarily offer explanations for its occurrence or persistence. Rather, they either invoke values present in some positive peace conceptions (e.g., justice) in a normative fashion or critique other theories or international political behavior for lacking those values.

Marxist theory is perhaps the closest alterative framework for positive peace concerns, based largely on the element of economic justice (Brewer, 1990). In its traditional formulation, war and conflict between states occurs when capitalist countries clash over markets and resources in imperialist expansions. The movement away from conflicts arises through the simultaneous or sequential replacement of economic elites within states, such that class divisions are eliminated. Together with equitable sharing of resources and the elimination of neoliberal institutions, states will live in harmony with one another. Marxism and its variants have proven to be more aspirational than explanatory either because of a lack of empirical referents or the significant conflict propensities of states that have declared themselves to follow Marxist principles.

The so-called English School (Bull, 1977; Dunne, 1998), positing a world society or international society, accepts anarchy in the international system, but is built on norms and rules that provide order in the system. Central rules are those of sovereignty and nonintervention. These, however, provide a basis for negative peace more than positive types. Variations in this school include those with the positive peace conceptions of human rights and justice embedded in societal rules and norms. It is not always clear though how these norms influence state-state interactions. Indeed, it is possible that such rules facilitate more hostile interactions and even military force if the right of humanitarian intervention (or Responsibility to Protect) is recognized.

Various other theoretical approaches—such as critical theory, postcolonialism, and some variants of feminist theory—raise positive peace concerns such as social justice, egalitarianism, and the economic development. The intent, however, is largely to critique existing theories for ignoring these concerns or to criticize existing international orders for denigrating them. There is not an attempt to construct causal explanations for how these are or might be achieved, and indeed positivist approaches to scholarly inquiry are usually eschewed.

Middle-Level Theories of Peace

Grand theories offer limited insights to the processes that produce and maintain peace between states. To understand peace as a central concern, it is necessary to consider theoretical formulations that specifically deal with peace, and that means shifting to what has been called middle-level theory rather than its grand cousins. Parts of the sub-discipline of peace studies provides such a focus, but many of its works are largely in the critical theory and normative traditions (e.g., Lederach, 2003) and therefore lack the capability of explaining how and why states become more peaceful (for an intellectual history, see Stephenson, 2010). Peace theory, as defined here, requires an argument, with evidence, that can account for how states can move from hostile relations to negative peace, and then most importantly from negative to positive peace. Empirically, the latter is recent and relatively rare (Goertz et al., 2016). We now review several prominent efforts in these tasks.

Functionalism and Regional Integration Theory

Although not formally a theory of positive peace, functionalist and neofunctionalist formulations have been around for decades, most prominently growing out of a desire to explain European integration. Nevertheless, Europe is an example (perhaps the only example) of a pluralistic security community, and thus accounting for its development provides insights into how positive peace can develop. In addition, integration is closely related to cooperation as part of peace. Deutsch and colleagues (1957) clearly lie within this tradition.

Functionalist theory (Mitrany, 1943) traces the road to deep cooperation, and therefore positive peace, with the necessary condition of common problems between states that require multilateral cooperation for solutions. Because of nationalist barriers to cross-border cooperation, the first steps to cooperation have to be taken outside of the political realm. Thus, initial cooperation would occur in “low politics” areas and largely through the efforts of technical experts rather than government leaders. If these were the only areas of cooperation, state-to-state cooperation would not occur and technical cooperation would not necessarily facilitate negative peace, much less promote the positive variety. Yet as cooperation produces beneficial outcomes, it is expected to generate spillover into other, ultimately more controversial or politicized, areas of mutual concerns. At the same time, public attitudes are thought to be more supportive of such collaboration and the supranational institutions when the outcomes are positive. Underlying this is the belief that people’s loyalties are rooted in performance satisfaction rather than national identity issues.

Original functionalist processes did not posit a central role for traditional political elites. Neofunctionalist modifications (e.g., Haas, 1964) assign these a greater role in the integration process and their support for such cooperation is important in the speed, depth, and breadth of the integration that results. Haas (1964) also noted another limitation on integration, namely, that the process was far more likely to occur on a regional rather than a global basis. Thus, positive peace was much likely to be found in multiple, geographically confined clusters than trans-regional networks.

Traditional functionalism implied a unidirectional, if not linear, process of how states become more peaceful. Empirically, this has not been true even in the European Union, which evolved in fits and starts. Nye (1971) aptly noted two important qualifications to the integration process. First, spillover from previous collaborative experiences can be either positive or negative; thus, cessations or reversals in the march toward positive peace can occur. Second, increasing interactions and cooperation does not necessarily lead to wider cooperation even as it might produce deeper cooperation in some areas. Thus, this provides a theoretical basis for understanding another brake on the road to integration. Other modifications included greater specification for how issues were linked and therefore facilitated spillover. The role of non-governmental organizations, beyond technical experts, was also given more prominence. Most notably, international institutions were thought to have a critical role (Moravcsik, 1997) in furthering integration.

The specifications just discussed detail the process by which positive peace and cooperation emerge, but it doesn’t offer much in terms of the conditions under which functionalist progress is more probable, except for the initial conditions of common problems that could not be unilaterally resolved. To fill this theoretical gap, Nye (1971) offered a series of conditions that facilitated integration and thereby clues to when and to what extent (rather than just how) positive peace would be formed. These included similarities across states in terms of economic capability, adaptive ability, and elite values among others. These set the stage for integration, but not all groups of states who share these traits will automatically become more integrated and peaceful. States need to perceive that integration provides a modicum of equal benefits to cooperation; low costs to integration are also facilitating conditions.

Functionalism and its variants provide a detailed account of how groups of states integrate and by implication how positive peace prospects are enhanced. Empirically, there has been less integration than might be predicted from the theory, and even the prototype of the European Union has not often followed the path described by the theory. There have been other regional “zones of peace” (Kacowicz, 1998), including in the Third World, but these have been characterized more by the absence of war than integration and are based on satisfaction with the territorial status quo. Functionalism also is largely silent on how hostile relationships are transformed such that integrative processes can commence.

Rivalry Termination

One set of works concentrates on how states move out of the most hostile of relationships—rivalries. The end state of rivalry termination, however, in these works is not clear in that the end of rivalry generally produces negative peace, but these relationships potentially run the gamut from very friendly relations (France and Germany in the 21st century) to those just short of full-scale rivalry (Israel and Egypt after Camp David). Nevertheless, these formulations offer insights into the establishment of negative peace and how some of the first steps to positive peace might occur.

There are a number of theoretical ideas about how rivalries end, and many focus on the emergence of some significant change that facilitates the termination conditions. Change might be found domestically in one or both of the rival states or in the external security environment. Most prominently, these changes are reflected in the punctuated equilibrium model (Diehl & Goertz, 2000), which begins with the expectation that once established, rivalry processes are difficult to alter. If rivalries are the result of well-entrenched causes, then the end of a particular rivalry should be associated with some dramatic change that disrupts established patterns of behavior. Diehl and Goertz (2000) argue that political shocks are virtual necessary conditions for the end of rivalries. These can occur at the system level, with world wars and major shifts in the power distribution among those shocks most cited. Shocks might also occur within either of the rival states, with civil wars and regime change thought to open the possibilities for rivalry termination. Most notably, shocks can lead to the rise of new alliances, sometimes with old enemies, in order to meet emerging threats. Domestic-level shocks can make ending rivalries a necessity to deal with internal problems or substantially change the policy preferences of the regime, such that the bargaining spaces and opportunities for ending rivalries are expanded.

Cox (2010) sees domestic policy failure as the instigator of the rivalry termination process. Failures in policy prompt changes in preferences, which in turn expand the bargaining space in which rivals can agree to end their competitions. The first component is domestic realignment that comes from a regime change or a new government within existing regime structures. Such changes stem from policy failures on the national level; problems stemming from national economic policy are a recurring theme. In this framework, simple regime change is not necessarily conducive to rivalry termination. The direction of the regime change is as critical as the domestic realignment itself. If one hawkish leader replaces another, then there is likely to be little impact on the rivalry. There must be a movement toward leadership that is “moderate” or “dovish,” leaders who are more willing to make concessions and reach compromise with an enemy.

Cox (2010) also argues that domestic realignment that leads to rivalry termination is less likely to produce changes in rivalry dynamics unless it is accompanied by foreign policy failure; domestic policy failure alone is not sufficient to alter rivalry dynamics, and foreign policy failures might not lead to changes in government if the domestic economy is healthy. The combined domestic and foreign failures are said to produce a greater willingness to accept rivalry concessions, thereby opening up the bargaining space with a rival and making some kind of accommodation possible.

What drives foreign policy failure or at least the reassessment of foreign policy preferences? There seems to be some consensus around the importance of multiple, simultaneous rivals. Bennett (1996) suggests that states might need to end one competition in order to concentrate on a new enemy. His analysis of rivalry termination also indicates that some rivalries end when the rivals begin to have common external security threats; in effect, the advent of new rivalries with negative links to extant rivalries causes the latter to end. Cox (2010) emphasizes the resource pressures that stem from multiple rivalries. He argues that resource strains emanating from multiple rivalries produce domestic policy failures as the government spends more on external rather than domestic needs.

Models of how rivalries end that depend largely on changes in one state run into the problem that rivalry termination is a joint decision (except for imposed military victories and total capitulations, outcomes that are relatively rare). Where does the second rival come in when the conditions for rivalry settlement arise in the first rival? Cox provides two answers, almost as an addendum to the basic argument. The first is that the preference change of the first rival might lead its set of acceptable resolutions to be enlarged such that its bargaining space of acceptable solutions now overlaps with that of its rival; unfortunately, this is difficult to observe prior to any agreement. Second, the other rival might also experience similar and simultaneous domestic and foreign policy failures, thereby making it more receptive to its opponent’s peace overtures.

An integrative specification of rivalry termination comes from Rasler, Thompson, and Ganguly (2013). They accept the proposition that rivalries are difficult to dislodge. That is, once established, it is very hard to move from rivalry to negative peace, much less more positive manifestations. Accordingly, they concur that some type of environmental shock might change rivalry dynamics. Shocks that affect the perceptions of external threat or influence actor capabilities will be the ones to prompt change. These must be major in any case, but the magnitude necessary is proportional to the degree to which rivalry dynamics and expectations are entrenched. Political shocks do not automatically move relationships in the direction of rivalry termination, but depending on the type of shock and its effects they could reinforce rivalries.

Extending beyond other theories of rivalry termination, Rasler and colleagues (2013) identify other sources for a reevaluation of perceptions of external threat and enemy capabilities—and thereby the strategies to deal with them: leadership change and third-party pressures. These are sources for preference change toward the rival. New leaders bring new ideas and strategies. Third-party pressures might also provide impetus for policy reevaluation, and could take on particular importance in the face of domestic political opposition to change.

Up to this point, the argument is monadic in that it primarily specifies processes in one of the rival states. Nevertheless, rivalry relationships involve two actors, and thus the actions of the enemy state are important in whether the rivalry persists or ends. Accordingly, Rasler and colleagues (2013) note that new strategies in the one rival need to be met with reciprocity from the other state in order for the peaceful processes to take hold. In addition, the strategies must produce a diminution of hostility (that is, they must demonstrate some success). Lacking reciprocity or such success, the strategies will likely be abandoned and the rivalry will persist.

Rivalry termination studies provide important insights into how state relationships are transformed in the direction of becoming more peaceful, but not necessarily peaceful in themselves. That is, we understand how states can transition away from rivalry, but the endpoint is not clear: What accounts for when the transition is merely negative peace as opposed to more cooperative relationships? The theories discussed here don’t answer this question. Nevertheless, empirically state relationships don’t jump from overly hostile to positive peace in one step or over a short period of time; rather, rivalry relationships most often transition to negative peace and positive peace relationship evolve from state interactions that were initially in the negative peace range (Goertz et al., 2016). Thus, even as rivalry termination theories are partial theories of peace, they are important pieces.

Beyond Negative Peace

Only a few formulations attempt to account for the full transformation of relationships across the continuum of the most hostile to the most peaceful. That is, they seek to do more than explain how negative peace develops out of rivalries, but also how positive peace relations occur as well.

Goertz and colleagues (2016) argue that the shifts from rivalry to negative peace and from negative to positive peace require different theoretical explanations. Although fundamentally a systemic analysis, their arguments are largely applicable in terms of dyadic relations as well. They claim that negative peace is a necessary, but far from a sufficient condition, for movement into the positive peace realm for states.

For the first shift, their theory is that the issues over which states fight is central to understanding state relationships; specifically minimizing or resolving territorial conflict is associated with the decline in rivalry. This is a function of both international norms prohibiting the use of force in resolving disputes as well as the increasing use of peaceful conflict management approaches when disagreements do arise.

They argue that there have been several significant normative changes, beginning early in the 20th century and coming to fruition after 1945; all involve the acquisition of new territory or the creation of new states. The first of these, the norm against conquest, is a prohibition against gaining territory through the use of military force. The anti-conquest norm took away many of the confrontations that formed the bases of rivalries and prevented the cycles of disputes and claims over the same pieces of territory that sustained those rivalries. Two other norms deal with the creation of new states in the international system, a process that was often violent itself but also carried with it a legacy of violent confrontation in future interactions with new state. The norm against secession was designed to prevent the breaking apart of states, except by the mutual consent of the rump state and the newly independent political entity. The norm of decolonization is that the transition from colony to independent state should be peacefully granted by the colonial power and not require the use of military force. The net effect of these three norms was to remove, or at least significantly diminish, military force as a mechanism to resolve territorial disputes. A fourth territorial norm, uti possidetis, calls for following previous administrative borders in setting new international boundaries. The result is that there are fewer territorial disputes when the norm is followed and uti possidetis provides a legal principle upon which new borders are drawn and delegitimizes attempts at altering those borders in the future. Collectively, “stable borders” facilitate the transition away from rivalry and stabilize relationships once they reach negative peace (Owsiak, Diehl, & Goertz, 2017).

International territorial norms have substantially taken military force off the table for territorial revision. States still make competing claims over large tracts of land and border delimitation. Without military force as a legitimate option, there must be peaceful alternatives to resolving these disagreements. The rise of mediation and legal approaches (adjudication and arbitration) has provided mechanism for states to resolve their disagreements peacefully.

Goertz and colleagues (2016) provide extensive empirical evidence for their model of the shift away from rivalry. The movement from negative peace to positive peace involves a different process and key conditions, however, and their theoretical formulation is less specified and more speculative. The shift from negative peace to positive peace requires a series of affirmative actions at cooperation rather than merely removing issues of contention. Accordingly, movement to positive peace is less likely than shifts from rivalry to negative peace and likely to be less abrupt than rivalry termination, for example. The elements of institution building, integration, and coordination not only take time, but require underlying shifts in public opinion, bureaucracy, and the like that are difficult to achieve at least in the short term.

Harkening back to functionalist logic, some geographic proximity might be a necessary condition for positive peace relationships to develop. Neighbors interact more with one another, positively and negatively, on a variety of dimensions and therefore there is the opportunity for collaboration and conflict. Geographic proximity also raises the possibility of common problems that could be solved by coordination and cooperative institutions, consistent with functionalist logic.

Beyond geography, other key factors in their argument are strong and legitimate institutions, both at the domestic and international level. With respect to the latter, interstate peace is created through strong institutions and organizations. A stress on peace and its geographic character leads to a focus on regional economic institutions (REIs). They formalize and guarantee commitments to coordinate interactions among members that are characteristic of positive peace—trade, communication, and various policy areas. Second, they do so in a wide range of issue areas, providing breadth in a peaceful relationship rather than isolated cooperation. Third, REIs deepen cooperation over time, extending beyond or spilling over from the original areas of integration and thereby have the potential to transform warm peace relationships into security communities, although this is by no means guaranteed. Fourth, they have a systemic effect, albeit regionally constrained, by permitting positive peace relationships among multiple pairs of states simultaneously; thus, the effect is systemic (albeit a regional system) rather than just confined to a single pair of states.

At the domestic level, positive peace is not a function of simple democracy, but rather high-quality democracy. High-quality democracies do more than meet some minimum standard for democracy, but score highly on multiple dimensions on what it means to be a democracy; such as political participation, transparency, and rule of law, among others.

Another integrative formulation is provided by Kupchan (2010), the title of which—How Enemies Become Friends—reflects the transformation from one end of the peace continuum to the other. Kupchan sees the end of rivalries and the formation of peaceful relationships as a process involving a series of steps. Prompting these steps is a “strategic predicament,” which can arise from multiple simultaneous rivals. A state might need to choose to accommodate one enemy in order to effectively deal with another.

The strategic predicament generates the first stage of reconciliation, a conciliatory gesture or concession to an enemy (“unilateral accommodation”). This action requires a positive response to get the cooperative “tit for tat” sequencing in motion. Thus, the second stage involves reciprocal and positive responses (“reciprocal restraint”) to such overtures by the other rival, often leaving the most difficult issues for later negotiation. Diplomacy takes over, and there are a series of gestures and actions over a period of years that reinforce the march toward peaceful relations. All disputes are resolved peacefully, without jeopardizing overall relations.

The process shifts from diplomats to the general public in a third stage. In a process seemingly to mirror neofunctionalism, cooperation extends to all sorts of political, economic, and social realms (“societal integration”). A variety of actors are involved, including government offices, private groups, and even individuals. These cooperative actions increase in both number and depth of cooperation. Domestic interests prod the process by lobbying or encouraging further collaboration.

The fourth and final phase (“generation of new narratives and identities”) involves an attitudinal transformation in the rival states in which peoples come to identify themselves as friends, rather than enemies. Kupchan argues that domestic political processes can derail the process, and somewhat surprisingly, economic interdependence has little effect in promoting rivalry termination.

What Kupchan calls stable peace results from a process from in which three conditions are present. First is institutional restraint, in which states accept limitations on their power in relations with the other state. This often comes from domestic limits on power, such as checks and balances and the rule of law. Nevertheless, democracy is not required as autocratic states can practice strategic restraint even if institutionalized restrictions are not present. Second is the presence of compatible social orders that are essential for deepening cooperation in multiple areas across societies. These elements include “the distribution of political power among different social classes; the distribution of political power among different ethnic and racial groups; and the organizing principles of economic production and commercial activity” (Kupchan, 2010, p. 7). Finally, stable peace requires cultural commonality. This is a socially constructed set of symbols and practices based on ethnicity, race, and religion. Thus, states are drawn to others that are already a lot like themselves on other dimensions.

Final Thoughts

The vast majority of international conflict research considers peace only as the absence of war, that is “negative peace.” Beyond that, there is little consensus what other elements constitute “positive peace,” even though there are some promising new formulations. The liberal peace literature theoretically moves toward a theory of peace; democracy, trade, and integration more generally form a potential theory of peace. Nevertheless, the emphasis is on negative peace because empirically the literature uses “absence of militarized disputes and war” as the definition of peace. Social constructivists, in general, have not been interested in peace. For example, there is a large literature on banning weapons, such as landmines, cluster mines, chemical and biological weapons, but the analysis of peace has not been on the constructivist agenda with few exceptions. Thus, scholars cannot rely substantially on existing international relations theory to understand the process of peace.

Theoretical approaches specifically devoted to peace are limited, but offer some promising avenues for development. The most developed areas are those that posit the conditions for “negative peace,” specifically those that consider how rivalry relationships are terminated. Recent formulations backed by empirical testing have provided a solid knowledge basis for understanding those processes. Less clear is how positive peace evolves out of negative peace. Functionalism and related approaches offered a number of promising ideas, but research on them was perhaps too closely tied to the European experience and in any case has garnered far less attention in recent decades than is merited.

Whatever theoretical innovations occur, they must be able to account for substantial changes over time. Rivalry terminations to negative peace now occur with some frequency and do so less commonly by coercive means than in previous historical eras (Rasler et al., 2013). Transitions to positive peace are also largely a post-1945 phenomena (Goertz et al., 2016) and have increased over recent decades. These trends represent new challenges for theory formulation about peace, but they signal the importance of efforts to account for these developments.


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