WPS8248 Policy Research Working Paper 8248 Polarization, Foreign Military Intervention, and Civil Conflict Suleiman Abu Bader Elena Ianchovichina Middle East and North Africa Region Office of the Chief Economist November 2017 Policy Research Working Paper 8248 Abstract In a behavioral model of civil conflict, foreign military interventions exacerbate religious polarization, leading intervention alters the resources available to warring groups to high-intensity conflicts in the Middle East and North and their probability of winning. The model highlights Africa region, but not in the rest of the world. These results the importance of distributional measures along with suggest that, unlike in the rest of the world, where civil the modifying effect of the intervention for conflict inci- conflicts are mostly about a public prize linked to ethnic dence. The paper confirms empirically the finding in the polarization, in the Middle East and North Africa they are literature that ethnic polarization is a robust predictor of mostly about a sectarian-related public prize. The results civil war, but it also finds evidence that religious polar- are robust to allowing different definitions of conflict, ization is positively and significantly associated with civil model specifications, and data time spans, and to con- conflict in the presence of foreign military intervention of trolling for other types of foreign military interventions. non-humanitarian and non-neutral nature. Such external This paper is a product of the Office of the Chief Economist, Middle East and North Africa Region. It is part of a larger effort by the World Bank to provide open access to its research and make a contribution to development policy discussions around the world. Policy Research Working Papers are also posted on the Web at http://econ.worldbank.org. The authors may be contacted at abubader@bgu.ac.il or eianchovichina@worldbank.org. The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent. Produced by the Research Support Team Polarization, Foreign Military Intervention, and Civil Conflict Suleiman Abu Bader and Elena Ianchovichina JEL classification: D74, D31 Keywords: Conflict, polarization, foreign intervention, Middle East and North Africa.  The findings, interpretations, and conclusions expressed in the paper are entirely ours and should not be attributed to the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent. We thank Shantayanan Devarajan, Aart Kraay, Bob Rijkers, Alexei Abrahams, and participants in a seminar, organized by the Chief Economist Office of the World Bank’s Middle East and North Africa region, the 11th Defense and Security Economics Workshop at Carleton University in Ottawa, Canada, the NBER Conference on the Economics of National Security in Cambridge MA, and the 13th Annual Workshop of the Households in Conflict Network in Brussels, Belgium, for useful comments on earlier drafts of the paper.  Suleiman Abu Bader is a senior lecturer in the Department of Economics at Ben-Gurion University of the Negev, Israel, E-mail: abubader@exchange.bgu.ac.il.  Elena Ianchovichina is a lead economist in the Chief Economist Office, Middle East and North Africa Region, the World Bank, 1818 H Street NW, Washington, DC 20433, USA, Tel: +1 202 458 8910, E-mail: eianchovichina@worldbank.org. I. Introduction Civil wars and other types of political violence have grave consequences for human development and global poverty reduction efforts. They disrupt economic activity and investments and destroy human lives and infrastructure, so their effect is usually felt long after peace is restored. The literature on armed insurgencies argues that countries at risk for civil wars tend to be poor (Fearon & Laitin, 2003), politically unstable (Hegre et al., 2001), abundant in lootable resources and unskilled labor (Collier and Hoeffler, 2004), and ethnically polarized (Montalvo and Reynal- Querol, 2005; Esteban, Mayoral and Ray, 2012). Except for the Republic of Yemen, the countries in the Middle East and North Africa do not fit this profile. Following independence, most Arab countries made substantial socioeconomic progress. Nearly all of them achieved middle-income status, reduced extreme poverty, kept vertical economic inequality at moderate levels, and improved access to education and health (Devarajan and Ianchovichina, 2017). Horizontal inequality was moderate as reflected by ethnic and religious polarization levels that were on average below those observed in other regions (Table 1). Following the tumultuous 1950s and part of the 1960s, most of the Arab states remained politically stable between the late 1960s to the early 2000s. Yet, during the same period (from 1965 to 2004), the average incidence of conflict by countries in the MENA region far exceeded the corresponding incidence in the rest of the developing world; it was one and a half times higher than the incidence of civil conflict in Sub- Saharan Africa, twice the incidence in Asia, and more than three times the incidence in Latin America and the Caribbean (Table 1). The high incidence of civil conflict in these mostly middle- income countries poses a puzzle, the so-called paradox of “political violence in middle-income 2 countries” (Ianchovichina, 2017). This paper explores one potential explanation for this puzzle: the role of non-humanitarian and non-neutral foreign military interventions.1 Table 1 Averages of some major indicators (per country per period) External Conflict Religious Ethnic (1)/(3)1 (1)/(4)2 (2)/(3) (2)/(4) Intervention Incidence Polarization Polarization Int_nh PRIOCW RELPOL ETHPOL (1) (2) (3) (4) (5) (6) (7) (8) MENA .370 .267 .470 .525 0.79 0.70 0.57 0.51 SAFRICA .166 .179 .701 .537 0.24 0.31 0.26 0.33 ASIAE .095 .136 .507 .458 0.19 0.21 0.27 0.30 LAAM .084 .086 .404 .646 0.21 0.13 0.21 0.13 Data sources: IMI data (Pearson and Baumann, 1993) for external military interventions of non-neutral and non- humanitarian type, Int_nh, in (1); PRIO for conflict incidence, PRIOCW, in (2); L’Etat des religions dans le monde and The Statesman’s Yearbook for religious polarization, RELPOL, in (3); WCE for ethnic polarization, ETHPOL, in (4). Note: MENA stands for Middle East and North Africa; SAFRICA is Sub-Saharan Africa; ASIAE is East Asia; and LAAM is Latin America. Columns (5) and (6) display numbers for the incidence of external intervention per unit of religious and ethnic polarization, respectively. Columns (7) and (8) display numbers for the incidence of civil conflicts per unit of religious and ethnic polarization, respectively. Previous studies of civil war incidence have emphasized different explanatory factors, but virtually all have related civil war to domestic factors and processes. Theoretical studies of internal conflict have focused on grievance-motivated rebellions (Gurr, 1970), the factors creating opportunities for collective action in mobilization (Tilly, 1978), and the role of rents from conflict in promoting support for violence (Collier & Hoeffler, 2004). Many studies have explored the hotly contested link between ethnic and religious diversity and social conflict. Fearon and Laitin (2003) do not find a link between ethnic heterogeneity and conflict, but others insist that ethnic cleavages may increase the risk of conflict (Ellingsen, 2000; Cederman & Girardin, 2007; Montalvo and Reynal-Querol, 2005) and the duration of civil wars (Collier, Hoeffler, and Soderbom, 2004).2 Arguing that there is less violence in highly homogeneous and highly heterogeneous societies, and more conflict in societies where a large ethnic minority lives side by 1 Other explanations for this puzzle, referring specifically to the period after the Arab Spring, are discussed in detail in Ianchovichina (2017). 2 Collier et al. (1999) argue that the duration of civil wars is positively, though non-monotonically related to the level of ethnic fractionalization of the warring society. The implication is that polarized societies would generate longer civil wars because the cost of coordinating a rebellion for a long enough period could be prohibitively high in very diverse societies. 3 side with an ethnic majority, Montalvo and Reynal-Querol (2005) show that ethnic polarization,3 not ethnic fractionalization,4 is a significant explanatory variable for the incidence of civil war. They conclude that ethnic polarization has a robust and significant explanatory power on civil wars in the presence of other indices of fractionalization and polarization, while the statistical significance of religious polarization depends on the particular specification. Esteban and Ray (2011) formalize theoretically the link between distributional measures and conflict incidence and test these links empirically in Esteban et al. (2012). Assuming no external intervention, they find that all three indices of ethnic distribution – polarization, fractionalization, and the Gini-Greenberg index – are significant correlates of conflict.5 This literature has largely overlooked the role of transnational factors on conflict incidence (Regan 2010), despite the importance given to these factors in popular accounts of civil wars (McNulty, 1999). The research on interventions has focused on three areas: (i) the effect of foreign intervention on civil war duration; (ii) foreign intervention’s effect on civil war resolution; and (iii) foreign intervention’s effect on peace keeping. Quantitative studies in the first strand of the literature, reviewed in detail by Regan (2010), produce strong evidence that external interventions tend to lengthen civil conflict (Elbadawi and Sambanis, 2000), irrespective of whether they are in the form of direct military involvement, military aid, economic assistance or sanctions, or whether they are designed to be neutral or to favor the government or the opposition (Regan 2000, 2002). Several explanations of this effect have been put forward, with the most popular explanation linked to expected utility (Lake and Rothchild, 1998; Regan, 2002). Foreign intervention provides the 3 Polarization measures capture the distance of the group distribution from the bipolar one where the population is split in half into two large groups. 4 Fractionalization measures capture the extent of diversity in a country or society. 5 This result holds under the assumption that the resources committed by the warring groups come only from individual efforts within countries and that each warring group’s probability of winning equals their population share (Esteban and Ray, 2011). 4 resources necessary for one or both sides to carry out insurgency, which lowers the opportunity cost of participating in the war (Collier and Hoeffler, 2004), potentially making rival groups optimistic about the likelihood of a military victory and creating commitment problems.6 The latter could arise because the intervention may reduce incentives for the side that benefits from outside assistance to credibly commit to the terms of a peace deal or to reach such a deal because of the greater number of veto players, especially in the case of multiple interventions on different sides of the warring groups (Cunningham, 2004). The second body of this literature finds evidence for the positive effect of foreign interventions that occur once a peace treaty has been signed on the successful resolution of these wars (Walter, 2002; Doyle and Sambanis, 2000; Hartzell, Hoddie, and Rothchild, 2001; Fortna, 2002; and Hartzell and Hoddie, 2003). Zartman (1989) argues that foreign intervention can create a ‘hurting’ stalemate during which both sides calibrate their expected utility and realize that they must negotiate an end to the war sooner rather than later. Foreign intervention can also help overcome information failures that prevent warring factions from reaching a settlement and shortening the duration of the war (Zartman, 1989, 1995; Brown, 1996; Lake and Rothchild, 1998; Doyle, Johnston and Orr, 1997) and help solve commitment (Brown, 1996) and implementation problems (Hampson, 1996). The presence of third-party guarantees reassures combatants that the treaty is credible and alleviates their safety concerns, making post-treaty demobilization possible and credible (Walter, 1994, 1997, and 2002). The third strand of the literature finds that external intervention reduces the risks of war recurrence once a peace deal is reached and implemented (Doyle and Sambanis, 2000; Fortna, 2002). However, only neutral (UN) and multidimensional7 peacekeeping operations have a positive effect on peace maintenance, according to Doyle and Sambanis (2000). Other types of outside interventions, 6 Fearon (2004) and Salehyan (2004) make similar arguments. 7 Multidimensional operations include involvement in economic reconstruction, institutional reform and election oversight. 5 including monitoring and observer missions, economic reconstruction/institutional reform, and peace enforcement, appear to have no effect on either the duration of the post-war peace or democratization. Few studies in the literature explore the question of how foreign interventions influence the incidence of civil wars and the results of these studies are mixed. Albornoz and Hauk (2014) find that interventions by global superpowers such as the U.S. are a sizable driver of domestic conflict, with the risk of civil war increasing under Republican governments and decreasing with the U.S. presidential approval ratings. Cetinyan (2002) finds that external support does not affect civil war incidence, but it influences the terms of settlement in the event conflict occurs. Gershenson (2002) also looks at this issue but in terms of sanctions, not direct military intervention. He finds that strong sanctions can compel the state to engage rebel demands whereas weak sanctions against the state can weaken the rebels’ position. Gleditsch (2007) examines how transnational contagion from neighboring states affects the risk of conflict in a country and concludes that regional factors strongly influence the risk of civil conflict. This paper explores the effect of foreign military intervention on the incidence and intensity of civil war. Our hypothesis is that non-neutral and non-humanitarian external intervention increases the risk of high-intensity conflict that results in many casualties. The question of how different types of outside military interventions affect the intensity of war is distinctly different from the questions explored in the existing literature on intervention, which focus on war duration effects8 and not on the causal link between intervention, war incidence and its scale, or how costly a war is in terms of human casualties. This issue is particularly relevant in the context of the increased incidence of high-intensity conflicts in the Middle East and North Africa after the Arab 8 Lengthy wars are not necessarily costly in terms of casualties. 6 Spring; the post-Arab Spring civil wars have led to many casualties and massive destruction (Ianchovichina, 2016). The paper focuses on non-neutral and non-humanitarian external interventions because we expect that this particular type of intervention has the potential to disturb the status quo in a country by increasing the incentives of different groups to raise resources for fighting and thus altering the groups’ probability of winning. We also believe that this type of intervention has the highest potential to increase the intensity of fighting and the associated casualties, as external support decreases the rebels’ dependence on local support and therefore their incentives to protect the local population. Figure 1 Distribution of Military Intervention Frequency by Type and Region 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 MENA SAFRICA LAAM ASIAE Neutral and humanitarian Non-neutral and non-humanitarian Data source: IMI data (Pearson and Baumann, 1993). The global International Military Intervention (IMI) data set, which provides information on events involving foreign military deployment in countries around the world, indicates that there are large differences in the incidence of external military interventions by type and region. Since 1965 the incidence of non-neutral and non-humanitarian interventions has been highest on average in MENA and lowest in Latin America (Figure 1). In Sub-Saharan Africa – the region with the 7 second highest incidence of non-neutral and non-humanitarian interventions – the average prevalence of foreign military interventions was less than half of that observed in MENA. By contrast, neutral and humanitarian interventions appear evenly distributed across regions. Appendix Table 1 provides a complete list of military interventions that have been classified as non-neutral and non-humanitarian in the IMI database and that have been implemented around the world following the end of World War II. The data suggest that nearly all MENA countries have been the target of military interventions, but the case of Lebanon – a multi-sectarian state – stands out. It illustrates the dynamics between external interventions, the onset of the Lebanese civil war and its intensification. Prior to the war, interventions occurred because following the ‘Black September’ 1970,9 the Palestine Liberation Organization (PLO) was pushed out of Jordan and established presence in Lebanon, disturbing the balance among different sects in the country. After 1970 interventions occurred in Lebanon in support of the Shia minority, which was pushed out of Southern Lebanon into the urban peripheries of Beirut.10 These interventions, occurring in the context of shifting population weights, led to increases in sectarian polarization and a struggle for political power, which resulted in a split into pro-Nasser Sunni Muslim camp and pro-Western Christian camp. Eventually, a confrontation erupted between the Lebanese Forces (LF)11 and the Lebanese National Movement (LNM) and sectarian violence escalated, leading to further interventions in a vicious cycle that grew into a large-scale conflict. 9 During the ‘Black September’ conflict, the Jordanian Armed Forces fought with the Palestine Liberation Organization (PLO) and forced it to relocate from Jordan to Lebanon. 10 The ruling Alawite minority in Syria viewed the Shia minority in Lebanon as a counterweight against the Sunni majority of Syria and the Palestinians. 11 The LF included the Maronite Christians and the LNM represented a coalition between Druze, Shia, Arab Nationalists, Socialists, Communists and Sunni Militias. The LNM had the support of the PLO. 8 The paper incorporates foreign intervention in a model a la Esteban and Ray (2011). In the model external intervention affects the probability of winning of warring groups12 and the resources available to them and therefore modifies the horizontal distributional measures. External interventions modify the effect of the distributional measures on the risk of conflict as they alter the balance of power among potential warring groups and therefore the incentives of groups to raise war-related resources. In other words, the revised model tells us that the equilibrium level of conflict depends on the distributional measures of inequality, fractionalization and polarization, modified to reflect the effect of military intervention. The theoretical specification does not indicate the direction and strength of the modifying effect– depending on the type of intervention and the presence of other interventions, it may increase or decrease the risk of conflict or it may have no effect on it. The theory informs the format of the empirical model, which allows us to estimate empirically the direction and strength of the intervention and its modifying effect. We rely on the global International Military Intervention (IMI) data set for data on different types of external military interventions, the Peace Research Institute of Oslo (PRIO) data set for civil wars, and the databases on ethnic and religious fractionalization used by Montalvo and Reynal-Querol (2005). Our findings are consistent with the results in the literature (Montalvo and Reynal-Querol, 2005; Esteban, Mayoral and Ray, 2012) that ethnic polarization is a robust predictor of civil wars. In addition, we find robust evidence that religious polarization is positively and significantly associated with civil conflict in the presence of non-humanitarian and non-neutral foreign military interventions. Such external interventions exacerbate religious polarization, leading to high- 12 The extent to which probabilities shift remains unknown to opponents due to asymmetric information and incentives to dissemble, creating conditions for violence (Fearon 1995). 9 intensity conflicts in the Middle East and North Africa region, but not in the rest of the world. We find no such effect in the case of neutral and humanitarian military interventions. The remainder of this paper is organized in the following way. Section II presents the theoretical model. Section III discusses the empirical model and data and Section IV presents the main econometric results. We discuss endogeneity issues and robustness checks in Section V and present a summary of findings and concluding remarks in Section VI. II. Theory We explore the equilibrium level of conflict attained in a behavioral model in which warring groups choose the amount of resources to commit to a conflict. In the model warring groups can receive external military assistance. This help may be extended for political, economic, or any other reasons and may come in the form of direct military assistance, i.e. a foreign army fighting on behalf of the warring group, or other assistance that alters the groups’ chances of winning.13 The model developed by Esteban and Ray (2011) defines the link between conflict and measures of inequality and polarization along non-economic identity markers such as ethnicity or religion.14 These divisions enable groups interested in stoking conflict to channel antagonisms into organized action. This paper argues that external military interventions may deepen perceptions of horizontal divisions and may alter the behavioral incentives of the warring groups to raise war- related resources. Leaving such influences outside the analysis may therefore overestimate the importance of distributional factors as reasons for civil wars. This paper does not study the motives 13 External assistance at one point can also give warring factions the assurance of support at a later time. However, the extent to which intervention alters the probability of winning remains unknown to opponents due to asymmetric information and incentives to dissemble (Fearon 1995). 14 Polarization may occur along other identity markers such as political ideas, racial, and/or social views. 10 behind intervention15 and does not represent explicitly the preferences of the intervening external parties;16 instead we consider the incentives of the domestic warring factions in the presence of exogenous interventions and in particular how foreign support may affect warring factions’ efforts to raise resources and change their probability of winning. We consider a country with a population of N individuals belonging to m warring groups. In each group i, there are Ni individuals and N=∑Ni, for i=1,…,m. We assume these groups fight over a budget whose per capita value is normalized to unity and that a fraction of it, λ, is available to produce public goods. The winning group enjoys both a public prize,17 whose value is given by λ, and a private prize, which is given as the remaining fraction of the budget and can be privately divided among the members of the winning group once it gets control over the resources.18 Using the private good as numeraire, uij is the public goods payoff to a member of group i if a single unit per capita of the optimal mix for group j is produced. Then, the per capita payoff to members of (1− ) the warring group i is + , if in case group i wins the war and in case some other group is the winner. We assume that > for all i, j with i≠j. This payoff difference defines the “distance” across groups: = − . Individuals in each group commit resources r to influence the conflict’s outcome. These resources include time, effort, risk, and finance. The income equivalent cost to such expenditure is c(r) where c is assumed to be increasing, smooth, and strictly convex, with c’(0)=0. If ri(k) is the contribution of resources by member k of group i, then Ri=∑ri(k) is the total of all resources 15 Foreign interventions may occur for a variety of reasons, some of which may be linked to aspirations for greater economic, political, and ideological influence in a given country. 16 The paper focuses on equilibrium conflict, not equilibrium intervention. 17 The public prize can be enjoyed by all members of the winning group regardless of its population size and includes political power, control over policy, ability to impose cultural and religious values, among other benefits. 18 The private payoff, with a per capita value μ, could be in the form of administrative or political positions, specific tax breaks, and bias in access to resources, among others. 11 committed by group i. The total of all societal resources devoted to the war is R=∑Ri, for i=1,…,m and assuming that R > 0, the probability of winning is given by pi=Ri/R. The more resources group i commits to the conflict the higher its chances of success. If an external force provides resources to faction i, then group i’s probability of winning will be higher than that suggested by the domestic resources available to this group. The overall expected payoff to an individual k in group i is given by the following ( ) expression: ( )=∑ + − ( ( )),19 where ni=Ni/N is the population share of group i. Individuals choose resources r so as to maximize a mix of their own payoff and the group’s payoffs: ( ) ≡ (1 − ) ( ) + ∑є ( ), (1) where α is altruism and is a nonnegative number. If α=0, individual k maximizes individual payoff, but if α=1 then k acts so as to maximize the group’s payoffs.20 Assuming that rj(l)>0 for some l that belongs to j and not i, the solution to the choice of ri(k) is completely given by the interior first-order condition: Δ = ( ( )), (2) where ≡ (1 − ) + and Δ ≡ + for all j≠i and Δ ≡ 0. According to this condition, the marginal cost of raising funds to fight equals the marginal benefit of fighting for any member of group i. Esteban and Ray (2011) show that a unique equilibrium exists and that in an equilibrium, according to condition (2) every individual k of group i makes the same contribution. 19 Since the private good is given in per capita terms, to divide it equally among the winning members of group i, the private good must be scaled up by N. 20 Under some circumstances, discussed in Esteban and Ray (2011), α may exceed 1. 12 If we denote the ratio of the win probabilities to the population shares as γi=pi/ni and the per capita resources spent on conflict as ρ=R/N, and assume that c(.) is a quadratic function,21 when we substitute for pi and ri in equilibrium condition (2) using the fact that in equilibrium all ri(k)=Ri/Ni, and sum over all i, condition (2) is transformed into the following expression: ∆ ( )= . (3) There may be a substantial difference between the probability of winning (pi=Ri/R) and the population shares (ni) of a warring group i due to foreign military intervention. Therefore, we do not follow Esteban and Ray (2005) who assume that pi=ni,22 implying that the behavioral correction factor γ equals 1. Since we do not assume that the probability of winning pi equals the populations shares ni, we allow γi to differ from 1. The intervention may change the relative sizes of warring groups, and therefore moderate the effect of polarization. It may also promote greater resource mobilization and risk taking thus incentivizing warring groups to engage in high-intensity and prolonged confrontations with each. In short, allowing γi to differ from 1 and opening the possibility that γi≠γj for i≠j, enables us to investigate how external military interventions may affect the probability of civil conflict. We substitute for and Δ in condition (3) and obtain the following expression: (1 − ) (1 − ) ( )= + + . (4) After substituting for γi and re-arranging, condition (4) can be rewritten as: 21 Given the assumption of quadratic cost function c(ρ)=0.5ρ2, it can be shown that c’(γρ)=γc’(ρ). 22 In other words, Esteban and Ray (2005) assume that there is no deviation of the win probability from the population share. 13 ( )( )( ) ( ) ( )= + + + (1 − ) , (5) where Ge is the Gini index modified to reflect the presence of intervention through the behavioral factor parameter γ: = . The polarization measure, Pe, is also modified by the intervention as follows: = . The fractionalization index F is the Hirschman-Herfindahl fractionalization index = (1 − )= and its modified version Fe is given as: = . The equilibrium per capita conflict condition in the presence of external intervention depends on the modified horizontal distributional measures Ge, Pe, and Fe. 23 This leads us to the following proposition. 23 With the intervention the probability of group i winning the war is not necessarily equal to the population shares (ni). 14 Proposition: Equilibrium per capita conflict24 in a country is determined by the three distributional measures: the Gini index, the fractionalization index, and the polarization index, modified by the influence of external military intervention as given in equilibrium condition (5). Proof: The discussion after (3) outlines the steps needed to prove that equilibrium condition (4) can be transformed into (5). If there is no external intervention (γj=1 for all j) condition (5) reduces to the condition (18) in Esteban and Ray (2011). Since irrespective of whether conflict is over private or public goods, external intervention affects the probability of winning of the warring groups and the resources they raise, altering their effective population sizes, it also moderates the effect of the distributional measures on conflict in a country. As in most cases the distance between groups = − is nonmonetary, it is challenging to arrive at a reasonable estimate of . For this reason, we adopt the approach in Montalvo and Reynal-Querol (2005) and assume that the distances between any pair of distinct groups are the same, with = 1 for all i≠j and = 0. This assumption allows us to simplify condition (5) and use the distributional measures of Montalvo and Reynal-Querol (2005) in the empirical parts of this paper. The simplified condition is: (1 − )(1 − )( − 1) (1 − ) ( )= + ( + (1 − ) ) + . (6) In this case, the equilibrium per capita conflict is determined by a combination of only two distributional measures of polarization (P) and fractionalization (F), and the influence of the intervention on these two types of distributional measures. 24 Equilibrium per capita conflict proxies for the equilibrium per capita resources spent on fighting on average in a country. 15 If the country is populous (i.e. N is large), as in the baseline case in Esteban and Ray (2011), condition (6) transforms into: ( )= ( + (1 − ) ). (7) This condition suggests that equilibrium per capita conflict in the large country case depends on the extent of fractionalization and polarization, and external intervention has an effect on equilibrium conflict only through its effect on horizontal polarization. If conflict is mostly over a public prize ( = 1), the equilibrium per capita conflict depends only on the polarization measure and the extent to which the intervention polarizes the society. This is consistent with the nature of the public prize, which is linked to the characteristics of the horizontal groups and the individual payoff from it, which is undiluted by one’s own group size. The public prize includes the seizure of political power, the setting of norms, the abolition of certain rights or privileges, the establishment of a religious state, the repression of a language and other public aspects that may lead to contention among horizontal groups. If conflict is mostly over a private prize ( = 0), the equilibrium per capita conflict depends only on the degree of fractionalization and not on polarization and/or external intervention. This is because the private prize is about access to resources (oil or specific material benefits obtained from special positions of power) and the individual payoff of this type of prize is diluted by the group size. In the general case, it is difficult to discern the effect of external intervention on civil conflict incidence without empirical testing, so next we test empirically the association between external military intervention and conflict prevalence. 16 III. Empirical investigation: Model and data We utilize a logit model for the incidence of civil wars: P ( PRIOCW it  1)    X 1it 1  1  X 2 it 1  2  Int _ nhis    it , (8) in which the independent variables, X1it1 and X2it1 , are the relevant distributional and control variables, respectively; and it is the error term. The distributional factors and some of the control variables are time invariant; the rest are set at their values in period t-1. The binary explanatory variable, Int_nhis, is 1 if there has been an external military intervention in at least one of the four years preceding period t (t-1≤s