Jack S. Levy
Department of Political Science, Rutgers University, New Brunswick, New Jersey 08901-1568; e-mail: jacklevy@rci.rutgers.edu
ABSTRACT
▪ Abstract I organize this review and assessment of the literature on the causes of war around a levels-of-analysis framework and focus primarily on balance of power theories, power transition theories, the relationship between economic interdependence and war, diversionary theories of conflict, domestic coalitional theories, and the nature of decision-making under risk and uncertainty. I analyze several trends in the study of war that cut across different theoretical perspectives. Although the field is characterized by enormous diversity and few lawlike propositions, it has made significant progress in the past decade or two: Its theories are more rigorously formulated and more attentive to the causal mechanisms that drive behavior, its research designs are more carefully constructed to match the tested theories, and its scholars are more methodologically self-conscious in the use of both quantitative and qualitative methods.
INTRODUCTION
The nuclear revolution, the end of the Cold War, the rise of ethnonational conflicts, and the spread of global capitalism and democracy have led to considerable speculation about a turning point in the history of warfare. Some foresee an “end of history” (Fukuyama 1992) and gradual obsolescence of war, or at least of great power war (Mueller 1989), whereas others see an explosion of low-intensity warfare and “clash of civilizations” (Huntington 1996). Each of these perspectives rests on some critical assumptions and theoretical propositions about the causes of war. My aim in this review is to assess the state of the art in our understanding of the causes of war.
Nearly 20 years ago two leading international relations scholars argued, from different perspectives, that our systematic knowledge of international conflict had progressed very little since Thucydides wrote his History of the Peloponnesian War (Gilpin 1981, p. 227; Bueno de Mesquita 1981, p. 2). That view was somewhat overstated at the time, because the field of international relations had made significant progress since its emergence by the end of World War II as an autonomous field of study, and it is certainly incorrect today. We are more explicitly theoretical in our general orientation, more rigorous in theory construction, more attentive to the match between theory and research design, more sophisticated in the use of statistical methods, and more methodologically self-conscious in the use of qualitative methods.1
However, we have few lawlike propositions, limited predictive capacities, and enormous divisions within the field.2There is no consensus as to what the causes of war are, what methodologies are most useful for discovering and validating those causes, what general theories of world politics and human behavior a theory of war might be subsumed within, what criteria are appropriate for evaluating competing theories, or even whether it is possible to generalize about anything as complex and contextually dependent as war.
This enormous diversity of theoretical, methodological, and epistemological perspectives on the study of war complicates the task of providing a concise assessment of the field. Because of the extensive coverage of my earlier review (Levy 1989b), I focus here primarily on significant developments in the last decade. This chapter begins with a theoretical overview, continues with a selective review and critique of some of the leading theories of the causes of war, and ends with a discussion of some general trends in the field.
The chapter's space limitations prevent discussion of several important new developments in the study of war and peace. I give limited attention to applications of game theoretic models (Powell 1990, Bueno de Mesquita & Lalman 1992, Morrow 1994, Fearon 1995) and say relatively little about cultural, constructivist, postmodern, and feminist approaches to the study of war and peace (Huntington 1996, Katzenstein 1996, Elshtain 1987). My citation of the literature is also selective. For more complete reviews and citations see Levy (1989b), Kugler (1993), Vasquez (1993). Some of the following builds on Levy (1997b).
THEORETICAL PRELIMINARIES
The Dependent Variable
International relations theorists generally define war as large-scale organized violence between political units (Levy 1983, pp. 50–53; Vasquez 1993, pp. 21–29). To differentiate war from lesser levels of violence, they generally follow the Correlates of War Project's operational requirement of a minimum (and an annual minimum) of 1000 battle-related fatalities (Singer & Small 1972). Peace, which is analytically distinct from justice, is usually defined as the absence of war.
Analysts traditionally distinguish international wars from civil wars, and interstate wars from imperial, colonial, and other international wars that involve non-state actors. Until recently they devoted a disproportionate amount of attention to great power wars, including “hegemonic wars.”3This great power and Eurocentric bias in the study of war is decreasing, however, in response to the end of the Cold War, the shift in warfare away from the great powers, and the rise of “low-intensity wars” and “identity wars” (Holsti 1996).4
Despite this consensus on what we are trying to explain, the question of what causes war can mean several different things (Suganami 1996). It can refer, first of all, to the question of what makes war possible, to the permissive or logically necessary conditions for war. These fundamental or primary causes of war explain why war repeatedly occurs in international politics, why war can occur at any moment. Thus scholars trace war to human nature, biological instincts, frustration, fear and greed, the existence of weapons, and similar factors.
Peace, however, is far more common than war, though as a “non-event” peace is difficult to measure. At the systemic level there may be more years characterized by war than by peace, but in nearly all war years most states are at peace, and at the dyadic level war is rare (Bremer 1992). This makes it hard to argue that human nature and related factors are causes of war. The point is that these factors are constants and cannot explain the variations in war and peace over time and space (Waltz 1959, Cashman 1993). If human nature varies, as some argue, then it is the sources of that variation, not human nature itself, that explain behavior. Moreover, even if human nature or biologically based instincts could explain aggressive behavior at the individual level, they cannot explain when such aggression leads to domestic violence, when it leads to scapegoating or other outlets, when it is resolved, and when it leads to international war.
The question of how to explain variations in war and peace is the second meaning of the broader question of what causes war. Why does war occur at some times rather than other times, between some states rather than other states, under some political leaders rather than others, in some historical and cultural contexts rather than others, and so on? This differs from still a third question: How do we explain the origins of a particular war?
Most international relations scholars (and particularly those in North America) focus primarily on the second question, explaining variations in war and peace. They leave the question of why war occurs at all to philosophers and biologists and leave the question of why a particular war occurs to historians. This is not to pass judgment on the relative importance of the three questions, only to say that they are different and that their investigation may require different theoretical orientations, different conceptions of causation and explanation, and different methodologies.
One important exception to this focus on variations in war and peace is the argument by Waltz (1979) and other neorealists that the fundamental cause of war is the anarchic structure of the international system. Anarchy, defined as the absence of a legitimate governmental authority to regulate disputes and enforce agreements between states, “causes” war in the sense that there is no governmental enforcement mechanism in the international system to prevent wars.5Although anarchy may provide one persuasive answer to the question of the permissive causes of war, it is generally treated as a structural constant and consequently it cannot account for variations in war and peace. Waltz (1988, p. 620) seems to concede this point and argues, “Although neorealist theory does not explain why particular wars are fought, it does explain war's dismal recurrence through the millennia.” Other neorealists also recognize this limitation and have begun to incorporate other variables—including the polarity of the system and the offensive/defensive balance—in order to explain variations of war and peace in anarchic systems.
Another exception to the focus on variations in war and peace can be found in some feminist theorizing about the outbreak of war, although most feminist work on war focuses on the consequences of war, particularly for women, rather than on the outbreak of war (Elshtain 1987, Enloe 1990, Peterson 1992, Tickner 1992, Sylvester 1994). The argument is that the gendered nature of states, cultures, and the world system contributes to the persistence of war in world politics. This might provide an alternative (or supplement) to anarchy as an answer to the first question of why violence and war repeatedly occur in international politics, although the fact that peace is more common than war makes it difficult to argue that patriarchy (or anarchy) causes war. Theories of patriarchy might also help answer the second question of variations in war and peace, if they identified differences in the patriarchal structures and gender relations in different international and domestic political systems in different historical contexts, and if they incorporated these differences into empirically testable hypotheses about the outbreak of war. This is a promising research agenda, and one that has engaged some anthropologists. Most current feminist thinking in political science about the outbreak of war, however, treats gendered systems and patriarchal structures in the same way that neorealists treat anarchy—as a constant—and consequently it cannot explain variations in war and peace.
The Levels-of-Analysis Framework
Ever since Waltz (1959) classified the causes of war in terms of their origins in the individual, the nation-state, and the international system (which he labeled first-, second-, and third-image explanations, respectively), international relations theorists have agreed on the utility of the levels-of-analysis framework as an organizing device for the study of war and international behavior more generally. Some scholars have modified Waltz's framework by collapsing the individual and nation-state levels to create a simplified dichotomy of nation (or unit) level and system level (Singer 1961, Waltz 1979), while others have disaggregated the nation-state level into distinct governmental and societal-level factors (Jervis 1976, Rosenau 1980), a practice that I follow here.
Following Waltz (1959), most scholars use the levels of analysis as a framework for classifying independent variables. This leads to such questions as whether the causes of war derive primarily from the level of the international system, national societies or bureaucracies, or individual decision-makers. Although the question of which level is most important has stimulated useful debate, until recently it distracted attention from the equally important issue of how variables from different levels interact in the foreign policy process.
The levels-of-analysis concept is sometimes used differently, to refer to the dependent variable, or to the type of entity whose behavior is to be explained. In this sense the systemic level of analysis refers to explanations of patterns and outcomes in the international system; the dyadic level refers to explanations of the strategic interactions between two states; the national level refers to explanations of state foreign policy behavior; the organizational level refers to explanations of the behavior of organizations; and the individual level refers to explanations of the preferences, beliefs, or choices of individuals.
The failure of scholars to be explicit about exactly how they are using the levels-of- analysis concept is a source of confusion in the field. Some have erroneously interpreted Singer's (1961, p. 92) comment that the various levels “defy theoretical integration…[and] are not immediately combinable” to suggest that analysts should not combine variables from different levels of analysis to explain foreign policy decisions or international outcomes. But Singer's statement makes sense only if the levels of analysis are conceptualized in terms of the dependent variable. This is the familiar micro-macro problem of aggregation across levels. We cannot assume that correlations or causal connections at one level of analysis are necessarily valid at another level. It is conceivable, for example, that concentrations of power may promote peace at the dyadic level but war at the system level.
This has important implications for theories of war and peace. Although it is possible that individual- or national-level variables could be the primary causes of war, these variables do not constitute a logically complete explanation because they do not explain how individual beliefs and preferences are translated into state decisions and actions or how the strategies or behaviors of states interact to lead to war as a dyadic or systemic outcome. To the extent that most wars involve the mutual and interactive decisions of two or more adversaries, an explanation for the outbreak of war logically requires the inclusion of dyadic- or systemic-level variables. This does not necessarily mean, however, that these variables are the most important in terms of amount of variation explained.
The levels-of-analysis framework is not the only way to organize the literature on the causes of war or on international politics more generally. It has long been fashionable for international relations theorists to frame debates in terms of the so-called paradigm wars between realism and liberalism (Baldwin 1993). In contrast to the realist focus on the struggle for power and security in an anarchic and conflictual Hobbesian world, the liberal tradition sees a more benign Grotian international society or Lockean state of nature where anarchy does not imply disorder. States have common as well as conflictual interests, aim to maximize economic welfare as well as provide for security, and create international institutions that help regulate conflict and promote cooperation (Keohane 1989). Although the paradigmatic debate between realism and liberalism has imposed some order on a chaotic field, it distracts attention from significant variations within each paradigm, variations that often lead to conflicting hypotheses. It also detracts from the important task of systematically integrating key components from each approach into a more complete and powerful theory. Furthermore, the “paradigm wars” ignore important hypotheses associated with the Marxist-Leninist tradition and saddle liberalism with charges of the neglect of power that are better associated with the utopianism of Thomas Paine and others (Walker 1998).
As a field, international relations needs to shift its attention from the level of paradigms to the level of theories, focus on constructing theories and testing them against the empirical evidence, and leave the question of whether a particular approach fits into a liberal or realist framework to the intellectual historians.
THEORIES OF THE CAUSES OF WAR
Systemic-Level Theories
The realist tradition has dominated the study of war since Thucydides, and includes Machiavellians, Hobbesians, classical balance of power theorists, Waltzian neorealists, and hegemonic transition theorists.6Although different realist theories often generate conflicting predictions, they share a core of common assumptions: The key actors in world politics are sovereign states that act rationally to advance their security, power, and wealth in a conflictual international system that lacks a legitimate governmental authority to regulate conflicts or enforce agreements.
For realists, wars can occur not only because some states prefer war to peace, but also because of unintended consequences of actions by those who prefer peace to war and are more interested in preserving their position than in enhancing it.7Even defensively motivated efforts by states to provide for their own security through armaments, alliances, and deterrent threats are often perceived as threatening and lead to counteractions and conflict spirals that are difficult to reverse. This is the “security dilemma”—the possibility that a state's actions to provide for its security may result in a decrease in the security of all states, including itself (Jervis 1978).
Realists do not assume that international relations are always conflictual, and they have recently focused on the question of the conditions for cooperation under anarchy, often through the use of iterated Prisoner's Dilemma models (Jervis 1978, Axelrod 1984, Grieco 1990). The iterated models are more appropriate for most situations than single-play Prisoner's Dilemma models, and the iterated Prisoner's Dilemma framework has generated some useful hypotheses regarding the rather restrictive conditions under which cooperation is likely. The assumption that the same game is repeated over and over is often problematic, however, particularly for security issues, because one play of the game (preemption, for example) can significantly change power relationships and affect payoffs in the next iteration. Nor is it clear that unilateral defection is always preferred to mutual cooperation; stag hunt models, in which mutual cooperation is both sides' first preference, may be more applicable in many situations (e.g. where each side fears both war and preemption by the other). There has been a tendency to apply Prisoner's Dilemma models to many situations in which the assumptions of the model are not satisfied.
The core proposition of realist theory is that the distribution of power, throughout the system or within a dyad, is the primary factor shaping international outcomes. But different versions of realist theory generate different, sometimes contradictory explanations and predictions of foreign policy choices and international outcomes, based on different assumptions about the motivations of states, the nature of power, and the identity and boundaries of the system. Given the variety of realist propositions and predictions, it is possible to interpret nearly any foreign policy behavior or international outcome as consistent with some version of realism. This is not particularly helpful, for if theories are not falsifiable they have little explanatory power. We should treat realism as a paradigm rather than as a theory, and focus instead on specific theories that generate more determinant, testable propositions.
The key division in the realist literature on war is not the standard one between classical realism and neorealism8, but rather between balance of power theory and hegemonic theory. Balance of power theory includes numerous variations on the classical realism of Morgenthau (1967) and the more systemic structural realism of Waltz. Hegemonic theory is a structural theory that incorporates power transition theory and hegemonic stability theory and that downplays the importance of anarchy.
Balance of power theory posits the avoidance of hegemony as the primary goal of states and the maintenance of an equilibrium of power in the system as the primary instrumental goal. The theory predicts that states, and particularly great powers, will balance against those states that constitute the primary threats to their interests and particularly against any state that threatens to secure a hegemonic position.9Balance of power theorists argue that the balancing mechanism—which includes both external alliances and internal military buildups—almost always successfully avoids hegemony, either because potential hegemons are deterred by their anticipation of a military coalition forming against them or because they are defeated in war after deterrence fails. In balance of power theory, serious threats of hegemony are a sufficient condition for the formation of a blocking coalition, which leads either to the withdrawal of the threatening power or to a hegemonic war.
Balance of power theory is more concerned with explaining national strategies, the formation of blocking coalitions, the avoidance of hegemony, and the stability of the system than the origins of wars, which are underdetermined. All balance of power theorists agree that some form of equilibrium of military capabilities increases the stability of the system (generally defined as the relative absence of major wars), and that movements toward unipolarity are destabilizing because they trigger blocking coalitions and (usually) a hegemonic war to restore equilibrium. There is a major debate, however, between classical realists, who argue that stability is further supported by the presence of a multipolar distribution of power and a “flexible” alliance system (Morgenthau 1967, Gulick 1955), and neorealists, who argue that bipolarity is more stable than multipolarity (Waltz 1979, Mearsheimer 1990).
Although neorealists rely heavily on polarity as a key explanatory variable, they do so with very little supporting evidence. They overgeneralize from the Cold War experience, where bipolarity is confounded with the existence of nuclear weapons and other key variables, and fail to demonstrate the validity of their arguments with respect to earlier historical eras. Although bipolarity is less common than multipolarity, it has occurred before, as illustrated by the Athens-Sparta rivalry in the fifth century BC and the Habsburg-Valois rivalry in the early sixteenth century, both of which witnessed numerous wars. Neorealists also ignore a number of quantitative studies that suggest that bipolarity is no less war-prone than multipolarity, that wars occur under a variety of structural conditions, and that polarity is not a primary causal factor in the outbreak of war (Sabrosky 1985).
An important alternative to balance of power theory is power transition theory, a form of hegemonic theory that shares realist assumptions but emphasizes the existence of order within a hierarchical system (Organski & Kugler 1980, Gilpin 1981, Thompson 1988). Hegemons commonly arise and use their strength to create a set of political and economic structures and norms of behavior that enhance the stability of the system while advancing their own security. Differential rates of growth, the costs of imperial overextension, and the development of vested domestic interests lead to the rise and fall of hegemons, and the probability of a major war is greatest at the point when the declining leader is being overtaken by the rising challenger. Either the challenger initiates a war to bring its benefits from the system into line with its rising military power or the declining leader initiates a “preventive war” to block the rising challenger while the chance is still available (Levy 1989b, pp. 253–54). The resulting hegemonic war usually generates a new hegemonic power, and the irregular hegemonic cycle begins anew. Power transition theorists disagree somewhat on the precise identity of hegemonic wars and the particular causal dynamics from which they arise; for comparisons of the wars and critiques of the theories see Levy (1985), Vasquez (1993).
Although many of the theoretical analyses of power transition theory focus on transitions between the dominant state in the system and a challenger, and include conceptions of a broader international system and hierarchy, some applications of power transition theory are dyadic in nature and apply in principle to any two states in the system. The dyadic-level “power preponderance” hypothesis, which holds that war is least likely when one state has a preponderance of power over another and is most likely when there is an equality of power, has received widespread support in the empirical literature (Kugler & Lemke 1996).
Balance of power theory and power transition theory appear to be diametrically opposed; the former argues that hegemony never occurs and that concentrations of power are destabilizing, and the latter argues the opposite. It is important to note that traditional balance of power theory has a strong Eurocentric bias and implicitly conceives of power in terms of land-based military power, whereas most applications of power/hegemonic transition theory focus on global power and wealth (Levy 1985). These different conceptualizations suggest the possibility that these two theories are not necessarily inconsistent; it is conceivable, for example, that the European system has been most stable under a balance of military power whereas the global system is most stable in the presence of a single dominant military and economic power.
This raises the relatively unexplored question of interaction effects between international systems at different levels. Rasler & Thompson (1994), for example, found that an increasing concentration of military power at the regional level often contributes to large-scale regional wars, but that these regional wars escalate to global wars only under conditions of a deconcentration of naval power and economic wealth at the global level. A similar question concerns the interaction effects between dyadic relationships and their systemic context. Geller (1993) found that dyadic power transitions are correlated with war under conditions of decreasing systemic concentration but not under conditions of increasing systemic concentration, where no dyadic transition war has occurred. These results suggest that the investigation of the interactive dynamics of nested systems is an important question for further research.
The relationship between economic interdependence and war is an old question that has attracted new attention in the past few years. Montesquieu [1977 (1748)] stated that “peace is the natural effect of trade,” and liberal economic theorists since Smith [1937 (1776)], Ricardo [1977 (1817)] have argued that capitalist economic systems and the free exchange of goods in an international market economy are the best guarantors of peace. Proponents advance a number of interrelated theoretical arguments in support of this proposition. The most compelling argument is that trade generates economic advantages for both parties, and the anticipation that war will disrupt trade and result in a loss or reduction of the welfare gains from trade or a deterioration in the terms of trade deters political leaders from war against key trading partners (Polachek 1980).10
Realists, including mercantilists and economic nationalists, advance a number of objections to the liberal economic theory of war. They often argue that the effect of trade on war is small relative to that of military and diplomatic considerations. They also question the liberal assumption that trade is always more efficient than military coercion in expanding markets and investment opportunities and in promoting state wealth. Although this assumption may be true in the contemporary system, at least for advanced industrial states, it is not universal; mercantilists correctly argue that military force has been an instrument to promote state wealth as well as power in certain historical eras (Viner 1948, Rosecrance 1986).
Realists downplay or reject the hypothesized deterrent and pacifying effects of the anticipated loss of welfare gains from trade. They argue that political leaders are less influenced by the possibility of absolute gains from trade than by concerns about relative gains, by the fear that the adversary will gain more from trade and convert those gains into further gains, political influence, and military power (Waltz 1979, Grieco 1990, Huntington 1993). Concerns over relative gains, bolstered by resource scarcities and domestic pressures, can lead to economic competitions and rivalries that under certain conditions can escalate to war (Choucri & North 1975).
In addition, gains from trade create dependence on one's trading partner. This dependence is often asymmetrical, and one party may be tempted to use economic coercion to exploit the adversary's vulnerabilities and influence its behavior regarding security as well as economic issues. These tendencies are reinforced by demands for protectionist measures from domestic economic groups that are especially vulnerable to external developments, particularly in bad economic times, and by leaders' temptations to bolster their domestic support through hardline foreign policies. These can lead to retaliatory actions, conflict spirals, and war.
Whether the incentives for the gains from trade dominate the incentives for coercion or protection based on economic asymmetries, and whether the latter escalate to trade wars and militarized conflicts, are empirical questions that analysts have only recently begun to analyze systematically. Although many find that trade is associated with peace (Polachek 1980, Oneal & Russett 1997), the relationship is modest in strength and is sensitive to measurement techniques and time periods analyzed. Some find that trade is associated with conflict (Barbieri 1996).11
Although liberals and realists disagree on the effects of trade on war, they appear to agree that trade and other forms of economic interchange between societies will cease or be drastically reduced once states are at war with each other. The liberal argument that trade advances peace is based on the premise that war eliminates or seriously reduces trade, and the realist emphasis on relative gains suggests that once war breaks out at least one of the belligerents will terminate trade in order to prevent its adversary from using the gains from trade to increase its relative military or economic power. Contrary to both liberal and realist expectations, however, there are numerous historical cases of trade between enemies during wartime, and a preliminary quantitative study suggests that war frequently does little to depress the volume of trade between adversaries (Barbieri & Levy 1997).
If validated by further research, this finding suggests a need for revisions in theories of interdependence, war, and peace. These theories are framed almost entirely at the systemic level and ignore the potentially important role of domestic variables. Self-interested domestic groups often press for the continuation of trade with the enemy, and governments often need tax revenues from trade and the general support of business groups in order to finance the war effort. Theories of interdependence and peace need to incorporate domestic variables into their hypotheses, refine their arguments regarding the deterrent effects of trade, and demonstrate these effects empirically. They also need to conceptualize relative gains at the systemic as well as the dyadic level; states often hesitate to terminate trade with the enemy for fear that they will lose that trade to a third party, who may be a greater economic or military rival.
The preceding reference to domestic variables applies to systemic-level theories more generally. Although the incorporation of domestic variables is certainly consistent with a broadened conception of liberal theory, it is less compatible with realist theories, which trace the sources of state behavior and international patterns to systemic-level structures of power. Although structural realist theories properly emphasize the constraints on action provided by the distribution of power at the systemic and dyadic levels, they fail to give adequate attention to state preferences and to the impact of domestic institutions, cultures, and informational considerations on both the preferences and the constraints of states. These omissions have led all but the most committed neorealists to conclude that systemic-level theories are theoretically incomplete and empirically inadequate, in that they leave too much of the variation in the outbreak and expansion of war unexplained. These conclusions have brought on increasing challenges to realism and other systemic-level theories, as well as a shift to the societal level of analysis.
Societal-Level Theories
After decades of giving less attention to domestic sources of international conflict than to systemic or individual factors, much of the action in the study of war is now taking place at the domestic level. Although interest in Marxist-Leninist theories has waned, there has been a tremendous growth of research on the relationships between regime type, particularly democratic regimes, and war (analyzed by Ray in this volume). Scholars have also devoted attention to the “diversionary” use of force for domestic political purposes, to the impact of ethnonationalism on international conflict, and to other domestic sources of international conflict. Although the literature on societal sources of international conflict is currently characterized more by collections of loosely- connected hypotheses than by well-developed theories, this work marks a significant advance in the study of war. This section focuses on diversionary theories of war and on theories of logrolling and coalition formation.
Liberal and Marxist theorists suggest that mass public opinion is inherently peaceful; if a state initiates a war it is usually because political leaders or the capitalist class choose war over the desires and interests of the public, or perhaps because of “false consciousness” on the part of the people. For example, the institutionalist explanation for the democratic peace—which suggests that the division of power within democratic states imposes institutional constraints on the use of force by political leaders—assumes that mass publics in any regime are less inclined than are political leaders to use military force.
This may be true, but little empirical research has been directed to this question. There are numerous historical cases in which the public appears all too eager for war, from the American Civil War to the eve of World War I in Europe to contemporary “identity wars.” In some cases this popular enthusiasm for war may push political leaders into adopting more aggressive and risky policies than they would have preferred. President McKinley, facing an escalating crisis with Spain in the 1890s, “led his country unhesitatingly toward a war which he did not want for a cause in which he did not believe” because of pressures from the public and the press (May 1973). There is substantial evidence that the outbreak of war, particularly victorious war, generally leads to a “rally ‘round the flag” effect (Mueller 1973) that enhances popular support for political leaders. Leaders often anticipate this “rally” effect and are sometimes tempted to undertake risky foreign ventures or hardline foreign policies in an attempt to bolster their internal political support.
This is the age-old “scapegoat hypothesis” or “diversionary theory of war” (Levy 1989a). It is theoretically grounded in social identity theory and the in-group/out-group hypothesis, which suggests that conflict with an out-group increases the cohesion of a well-defined in-group (Coser 1956, J Stein 1996). Group leaders are aware of the cohesive effects of external conflict and sometimes deliberately create or maintain external conflict to serve their internal purposes. As Bodin argued, “the best way of preserving a state, and guaranteeing it against sedition, rebellion, and civil war is to…find an enemy against whom [the subjects] can make common cause” (quoted in Levy 1989a, p. 259).
Empirical research on the scapegoat hypothesis has progressed through several stages. Early work by Rummel and others used factor analysis to determine empirical associations between the incidence of internal conflict and the incidence of external conflict. The finding that “foreign conflict behavior is generally completely unrelated to domestic conflict behavior” (Rummel 1963, p. 24) led to efforts to control for regime type and other variables that might affect the relationship between internal and external conflict (Wilkenfeld 1973). Although these controlled studies generated some positive findings, few of the correlations indicated strong relationships and there was little consistency across studies.
The absence of significant findings regarding the relationship between internal and external conflict contrasts sharply with evidence of external scapegoating from historical and journalistic accounts and from a growing body of case-study evidence. This discrepancy, together with the perceived inadequacies of the Rummel paradigm (Levy 1989a),12has led to a number of major research projects over the last decade on the politically motivated use of force. These studies have attempted to specify theoretical models that link domestic politics with the external use of force and to identify empirically the internal conditions under which the use of force is most likely.
Scholars have devoted particular attention to the timing of economic cycles and electoral cycles (in democratic states) and to existing levels of political leaders' domestic political support. The basic hypothesis is that the political insecurity of elites, and hence their propensity to use military force abroad, should be greatest during periods before elections, during periods of poor economic performance, or at other times when domestic political support is low.13These hypotheses find some confirmation in empirical tests over the Cold War period based on levels of inflation and unemployment (often combined into a “misery index”) to tap poor economic performance (Ostrom & Job 1986, Russett 1989), although the effects of the electoral cycle have been questioned (Gaubatz 1991). There has also been extensive empirical support for the hypothesis that external conflict does trigger a substantial rally effect, which generally diminishes over time (Russett 1990).
Most of these studies have focused on democratic regimes, partly because of the ease of measuring elite support levels but also because of the assumption that the greater political accountability of leaders in democratic states makes them more likely than authoritarian leaders to engage in external scapegoating. Autocrats too must maintain their basis of support, however, even if among more narrowly defined groups such as the military and economic leaders. Thus some argue that scapegoating may be as common among autocratic as among democratic leaders, and indeed some classic examples of scapegoating involve nondemocratic regimes (Argentina in the Malvinas, Germany in World War I, and Russia in the Russo-Japanese War, for example).
Whether the diversionary use of force is more common (or more effective) in democratic or authoritarian regimes depends on the potential benefits of scapegoating, the probability of a diplomatic or military victory, the domestic costs and risks, and the availability of alternative means of dealing with domestic opposition. Democratic leaders who initiate unsuccessful wars are thrown out of power much more frequently than are nondemocratic leaders (Bueno de Mesquita & Siverson 1995), but the personal costs of being removed from office may be greater for authoritarian leaders. Gelpi (1997) hypothesizes that the option of domestic repression is less available to democratic leaders and finds that democratic states were more likely than authoritarian regimes to initiate the use of force between 1946 and 1982. Another possible strategy for dealing with domestic oppositions is to secure additional resources from external allies, either to distribute among the disaffected members of society (or at least among key support groups) or to enhance the means of repression (see Barnett & Levy 1991, Bronson 1997).
Gelpi's (1997) finding raises interesting questions for the democratic peace and for international conflict more generally (Ray 1995, 1998). It challenges the hypothesis that democracies are more peaceful than are nondemocratic states and the assumption that wars between the two are generally initiated by the latter. This finding also leads to the dyadic-level questions of how frequently democratic scapegoating is directed at other democracies, and why the ensuing militarized dispute almost never escalates to war.
The more general question, which has been neglected in the literature, is what kinds of adversaries make good targets for diversionary action.14Scapegoating might be a particularly useful strategy for leaders of states engaged in enduring rivalries, and its use might help explain the intensification of rivalries, but the literature on enduring rivalries says little about this (Diehl 1998). Ethnic adversaries also make excellent scapegoats. Although students of ethnonationalism recognize the use of scapegoating by “ethnic entrepreneurs” to maintain and increase their own domestic support, theorists of diversionary behavior and theorists of ethnonationalism have made few attempts to build systematically on one another's conceptual frameworks or empirical knowledge.
Most theoretical and empirical studies of the diversionary use of force assume the existence of a unified political elite attempting to increase its support among a mass public that is susceptible to symbolic appeals to the interests and honor of the nation. Neither elites nor masses are necessarily unified, however, and some research explores the consequences of these divisions. Political leaders have different kinds of constituencies in different types of political systems, and in their diversionary use of force they may be more concerned about their support among some groups than among the public as a whole. Morgan & Bickers (1992), for example, find that the use of force by the United States is more related to levels of partisan support than to overall levels of support.
Elites are also divided, and one faction may support a policy of external scapegoating as a means of advancing its own interests in intra-elite bargaining and struggle for power (Lebow 1981). Alternatively, external scapegoating may be a means of unifying a divided elite. The Argentine plan to seize the Malvinas by force, for example, was designed not only to recover public support for the junta but also to give a divided regime a mission around which it could coalesce.
There is an interesting divergence between explanations of why political elites engage in external scapegoating and explanations of why scapegoating works to enhance or maintain their domestic support. The literature suggests that leaders adopt scapegoating as a rational instrument of policy to advance their interests, while publics respond on the basis of symbolic and emotional appeals, as explained by the in-group/out-group hypothesis. While the psychological rather than interest-based response of publics is certainly plausible, it is also possible to construct an interest-based or integrated explanation for the response of the public to the external use of force.
Recent research has attempted to integrate the behaviors of both leaders and publics into principal-agent and other rational choice models. In the basic model, the public and other key social groups are the constituents or principal, which has a choice as to whether to retain its agent, the political leadership. This choice is a function of the extent to which the principal's interests are advanced by the agent, which is often measured in terms of the success of both economic policy and the use of force in foreign policy (though other measures are possible). Constituents' choices are made in the context of uncertainty, given information asymmetries favoring the agent, and they must infer the agent's “type” (competent or not) from a combination of current foreign policy outcomes and their own prior probability estimates based on past economic performance. Agents understand this “signaling game,” so that even incompetent leaders may have the incentive to engage in risky foreign policy behavior in order to give the impression of competence. Analysts solve for the equilibrium and test it against the evidence (Richards et al 1993, Smith 1996).
These models help to explain “gambling for resurrection” through risky foreign policies by poor leaders who expect to be removed by their constituents (Downs & Rocke 1995). Although some of the assumptions of these models are rather strong, and although the classification of agents as either competent or not regardless of issue area is troubling, these attempts to model diversionary processes in terms of self-interested behavior of leaders and constituencies are a promising area for future research.
It is important to note that these models of diversionary processes (both formal and nonformal) are all models of foreign policy, not strategic interaction (and thus are not technically models of war). This raises the question of how external actors perceive and respond to diversionary actions. Do states recognize when another's behavior is driven by diversionary motives? If so, do they treat these actions differently than they do other actions and respond to them in different ways? In addition, do they anticipate when the adversary's domestic conditions make it particularly likely to engage in external scapegoating or other hardline foreign policies, and do they adjust their own behavior accordingly? Do they anticipate domestically induced preferences for conciliatory behavior by their adversaries, and do they attempt to exploit the adversary under such conditions? There is little attention in the literature to the strategic dimension of diversionary behavior or of domestic sources of foreign policy more generally, though Morrow's (1991) model of arms control negotiations and Smith's (1995) model of diversionary theory are important exceptions. The incorporation of a strategic component into diversionary theory is an important task for future research.
These rationalist models of aggressive foreign policies by self-interested elites faced with rational publics are also reflected in the traditional literature. Lenin's (1916) explanation of World War I as an attempt by the imperialist classes “to divert the attention of the laboring masses from the domestic political crisis,” for example, assumed rationality on the part of key domestic constituencies as well as the ruling class. Imperialist expansion works, for a time at least, by propping up the falling rate of profit and providing the ruling class with extra resources that they can use to secure the support of the leadership of key labor groups (in Levy 1989a, pp. 259, 280).
Marxist-Leninist models of imperialism, like models of scapegoating, implicitly assume that external expansion and the use of force serve the interests of the ruling class or elite but not those of society as a whole. If society benefited from expansionist foreign policies then a rational unitary model of the national interest would suffice to explain behavior and a distinctive societal component would not be necessary. The basic argument is that the benefits of expansion go to the ruling elite (whether Lenin's monopoly capitalists or Schumpeter's military-feudal elites), who have concentrated interests, while the costs of expansion are diffused throughout society in the form of taxation.
If the costs of aggressive foreign policies are too high—and we have enough examples of “imperial overstretch” to suggest that they sometimes are—it is not clear how elites maintain their power. As Snyder (1991) argued, groups concentrated enough to benefit from overexpansion are too narrow to control state policy, while those broad enough to control policy are too diffuse to reap benefits from overexpansionist policies. Snyder (1991) developed an alternative model in which key internal groups have parochial interests that favor different but limited forms of imperial expansion or military buildups. They secure and share power through logrolled coalitions and pursue the foreign policy interests advocated by each, so that the resulting policy is more aggressive or expansionist than that desired by any single group and cannot be supported by existing societal resources. The coalition of iron and rye in Germany a century ago is a classic example: The industrialists sought a more active role for Germany in the world economy and an expansion of the navy to back it up, while agrarian interests sought protection against Russian grain exports. The former alienated Britain and the latter alienated Russia, and Germany lacked the resources to deal simultaneously with both of these adversaries.
For Snyder, this rationalist model of logrolling is not sufficient to explain overexpansion or the stability of the ruling coalition. He argues that coalitions reinforce their positions of power and rationalize their policies by exploiting their control over information through the propagation of self-serving myths about their nation, its adversaries, and their history (Van Evera 1990–91). They then present these myths as lessons of history. These dynamics of overexpansion are most likely to arise in cartelized political systems and least likely to occur in democratic systems, where diffuse interests and the absence of information monopolies work against strategic myth-making.15
Individual-Level Theories
Individual-level theories assume (a) that external and internal structures and social forces are not translated directly into foreign policy choices; (b) that key decision-makers vary in their definitions of state interests, assessments of threats to those interests, and/or beliefs as to the optimum strategies to achieve those interests; and (c) that differences in the content of actors' belief systems, in the psychological processes through which they acquire information and make judgments and decisions, and in their personalities and emotional states are important intervening variables in explaining observed variation in state behaviors with respect to issues of war and peace.
There is a substantial literature on political leaders' “operational codes” and belief systems, on the influence of “lessons of history” on their beliefs and policy preferences, and on the role of misperceptions and biases in information-processing that affect crisis decision-making (George 1969;, Jervis 1976, 1988;, Lebow 1981;, Holsti 1967, 1989;, Levy 1994). A central theme in many of these models is that, because of cognitive limitations, decision-making is characterized by “bounded rationality” rather than the ideal-type rationality posited by formal decision theory. I limit my attention here to prospect theory, which is one of the most recent attempts to apply a social-psychological model to international relations but which shares some elements of more formal rational choice models. Kahneman & Tversky (1979) developed this theory of individual choice under conditions of risk to explain experimental anomalies in expected utility theory.
Prospect theory assumes that people evaluate outcomes in terms of deviations from a reference point or aspiration level rather than in terms of net-asset levels. They generally overweight goods in their possession relative to comparable goods they do not own (the endowment effect), overweight losses from that reference point relative to equivalent gains (loss aversion), and make risk-averse choices among gains but risk-acceptant choices among losses. People also overweight certain outcomes relative to merely probable ones and low-probability outcomes relative to other outcomes. This asymmetry of behavior with respect to gains and losses means that the way people frame their reference point in any given choice problem is critical. It is also subjective, although people tend to adjust psychologically to gains much more quickly than to losses and thus to frame around new acquisitions but not around recent losses.
These assumptions lead to a number of hypotheses about behavior with respect to international relations (Levy 1997a). (a) There is a “reference point bias” in behavior, a greater tendency to move toward the reference point than one would predict on the basis of standard expected-value calculations. When the reference point is the status quo, as it commonly is, there is a status quo bias in decision-making. (b) State leaders take more risks to maintain their international positions, reputations, and domestic political support than they do to enhance those positions. (c) After suffering losses (in territory, reputation, domestic political support, etc), political leaders do not adapt to those losses and renormalize their reference points but instead take excessive risks (relative to expected value calculations) to recover those losses. After making gains, political leaders adapt to them, renormalize their reference points, and take excessive risks to defend those gains against subsequent losses. Thus if A loses territory to B, A will take excessive risks to maintain her gains while B will take excessive risks to recover her losses. (d) Because adaptation to losses tends to be slow, sunk costs frequently influence decision-makers' calculations and state behavior.
With respect to strategic interaction, (e) the endowment effect leads actors to overvalue the concessions they give relative to those they get in return, leading to a “concession aversion” or a bias against agreements (relative to an expected-value calculus). (f) It is easier to deter an adversary from taking an action than to compel him to terminate an action or to undo what he has already done, and it is easier to deter an adversary from making gains than to deter her from recovering losses. (g) It is easier for states to cooperate in the distribution of gains than in the distribution of losses.
These are intriguing hypotheses that appear to resonate in the world of international relations, but several conceptual and methodological problems complicate the task of testing these hypotheses empirically. The problem of identifying the actor's reference point, particularly in the absence of a theory of framing, makes it very difficult to rule out the alternative and more parsimonious hypothesis that behavior is driven not by framing, loss aversion, and the reflection effect in risk orientation, but rather by a standard expected-value calculation (Levy 1997a).
CONCLUSIONS: GENERAL TRENDS IN THE STUDY OF WAR
There are general trends in the study of the causes of war that cut across different theoretical perspectives, some in response to real-world trends and others to autonomous shifts in intellectual paradigms. One is a partial move away from a long-standing great power focus toward a greater emphasis on small state conflicts, particularly on civil wars and ethnonational conflicts. There has also been a pronounced shift away from the systemic level (in terms of both independent and dependent variables), in part because of growing dissatisfaction with the failure of structural systemic models to explain enough of the variance in war and peace. This shift has led to rising interest in both dyadic-level behavior and societal-level explanatory variables.
At the dyadic level, in addition to long-standing research on dyadic power relationships and power transitions, there are new research programs on enduring rivalries, bargaining, territorial contiguity, trade, and other relationships. Some of these have generated much stronger empirical findings than those for systemic patterns or national-level behavior. Bremer (1992), for example, demonstrates that the probability of war is 35 times higher for contiguous dyads than for noncontiguous dyads for the 1816–1965 period, and Vasquez (1996) shows that when war occurs, a strong tendency exists for contiguous states to fight dyadic wars and for noncontiguous states to fight multilateral wars.16
Whatever the relationship between concentrations of military and economic capabilities at the systemic level, there is substantial evidence that at the dyadic level an equality of capabilities is significantly more likely to lead to war than is than is a preponderance of power (Kugler & Lemke 1996); bargaining strategies based on reciprocity are more likely to lead to peaceful outcomes than those based exclusively on coercive threats (Leng 1993); and “asymmetries of motivation” are at least as important as power differentials in determining outcomes of international disputes (George & Smoke 1974).
The shift to societal-level explanatory variables is a response to their long neglect in the literature; to the decline of systemic imperatives arising from the bipolar Cold War structure; to the increasing salience of smaller, politically unstable states and ethnonational conflicts in the post–Cold War world; and to the availability of good quantitative data on key variables (Gurr 1989). Interest in the societal level has also been spurred by the striking finding that democratic states rarely if ever go to war against each other, which “comes as close as anything we have to an empirical law in international relations” (Levy 1989b, p. 270).
There has also been an increasing recognition of the complexity of the causes of war and an increasing willingness to attempt to model that complexity. This recent interest in complexity, exemplified by Jervis' System Effects: Complexity in Social and Political Life (1997) and by Axelrod's Complexity of Cooperation (1997), involves more attention to multilevel explanatory frameworks, dynamic processes, reciprocal causation, endogeneity problems, and selection effects.
In the past decade most international relations theorists have moved beyond their earlier preoccupation with explanations at a single level of analysis and debates about which level provides the most powerful explanations. They now give much more attention to interaction effects among variables at different levels in the processes leading to war. Game-theoretic models, for example, which six or seven years ago were applied almost exclusively to problems of strategic interaction between states, now incorporate domestic structures and processes as well.
Applications of game-theoretic models have themselves become more sophisticated and more complex.17Prisoner's Dilemma and related 2 × 2 games were useful for the analysis of simple strategic situations, but the move to extensive-form games, particularly sequential games with incomplete information, marks a profound theoretical advance. The greater realism of the new models has contributed to a strong revival of interest in game-theoretic approaches in recent years. These games incorporate the uncertainty that decision-makers routinely face, the sequence of choices and counter-choices that generally characterize the outbreak of war, the problem of the credibility of commitments in an anarchic world, and the dynamics of signaling.
The conceptualization of international relations and war as a sequence of choices, which has long been common in the qualitative literature, is also reflected in much of the quantitative empirical literature. Early studies in the “correlates of war” tradition looked for simple empirical associations between systemic structures and the frequency and severity of war, reflecting the rather static balance-of-power propositions that they were designed to test. This research tradition has evolved such that it now conceptualizes international conflict as a process or series of steps (Vasquez 1993) from background conditions to the occurrence and evolution of militarized disputes to the outbreak and evolution of international war, which in turn affect background conditions (Bremer 1992, Cusack 1996). This more dynamic conceptualization led to the development of new data sets on militarized interstate disputes (Jones et al 1996), the Behavioral Correlates of War (Leng 1993), and international crisis behavior (Brecher et al 1988). These data sets have further facilitated analyses of the sources, dynamics, and consequences of international dispute and crisis behavior. The more dynamic character of theorizing about war is also reflected in the literatures on long cycles, power transitions, enduring rivalries, learning, and evolutionary processes.
The increasing complexity of theories of war and peace is reflected in the recognition of the importance of unintended consequences, endogeneity effects, and selection effects, as well as in the construction of rational choice and systems models that facilitate the analysis of such effects. In addition to placing greater emphasis on strategic behavior and interconnectedness of systems, scholars increasingly acknowledge that earlier modeling of actors' responses to exogenous events, institutions, and other external shocks neglected the possibility that those events or institutions were themselves the endogenous result of conscious strategic behavior. Many studies of deterrence, for example, conclude that the impact of military power differentials on crisis outcomes is often modest, but ignore the fact that such power considerations may have determined whether an actor initiated the crisis in the first place (Levy 1989b, p. 243). Extensive-form games facilitate the modeling of these dynamics (Fearon 1994, Bueno de Mesquita 1996).
There has been significant progress in the empirical study of the causes of war. Most empirical research is more theoretically driven than it was two decades ago. It is also characterized by a better match between theory and research design. We find fewer “barefoot empiricist” fishing expeditions and fewer idiographic single-country case studies. Large-n statistical studies now regularly employ such methods as event-count models, logistic regression, survival models, and interrupted time series, the assumptions of which better match the underlying theory and the nature of the data.
Case-study research is also more methodologically sophisticated. Influenced by George (1982), King et al (1994), qualitatively oriented scholars have made increasing efforts to deal with standard problems of scientific inference. Case selection is more likely to be driven by theoretical considerations and by the need to maximize control over extraneous variables than by substantive interest alone. Case-study research has become more historical, but it has also become more analytical and comparative. Graduate training programs have increasingly begun to include courses on qualitative methods as well as quantitative methods.
Another positive trend is toward the adoption of multi-method research designs, either in a single study or in a broader research program. Two decades ago, relatively few studies combined decision or game-theoretic models with statistical tests, but this is the norm today. There are also more and more studies that combine case studies with statistical analyses. Although some regard rational choice and case studies as antithetical, the combination of quantitative and qualitative research designs in the testing of rational choice theories allows each method to compensate for the limitations of the other. The combination of large-n statistical studies, case studies, and game-theoretic models by numerous scholars studying the interdemocratic peace and the diversionary theory of war provide examples of the potential of a multi-method approach, and the cumulative results have been far more convincing than those produced by any single method.
Whatever one's assessment of the state of the art in the study of war one or two decades ago, there are considerable grounds for optimism today. Although theoretical and empirical research in the field is more diverse and contentious, almost everything has improved. Our theories are more imaginative, rigorous, and relevant; our research designs are more closely matched to our theoretical propositions and more sensitive to potential problems of inference; our data sets are more numerous and more refined. Whether we have approached a turning point in the history of warfare is still a matter of debate, but we have clearly improved our understanding of the motivations, conditions, and processes that contribute to war or peace.
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