Journal of Peace Research

Recent formal and empirical research in political science and economics strongly indicates that various forms of political and social polarization increase the risk of violent conflict within and between nation states. The articles collected for this issue explore this crucial relationship and provide answers to a variety of topics: First, contributors address how institutions and other contingent factors mediate the conflict potential in polarized societies. Second, this special issue compares the explanatory power of income polarization with traditional and new measures of inequality. Third, the contributions examine how groups form and coalitions are built in polarized societies and how this affects political decision-making. Finally, the special issue analyses the interconnections between interstate war, internationalized conflict and polarization. This introduction synthesizes the literatures that have been developed on the issue of polarization and conflict in the various social scientific disciplines. The authors particularly discuss the similarities between economic models of conflict and the so-called crisis bargaining literature which has been mainly developed within political science. The article shows the differences between `polarization' and `inequality' and introduces the various measures of diversity that have been used in the study of interstate and intrastate conflict during the past few decades.

Recent large-N studies of civil war conclude that inequality does not increase the risk of violent conflict. This article argues that such conclusions may be premature because these studies, which usually test the conflict potential of `vertical inequality' (i.e. income inequality between individuals), tend to neglect the group aspect of inequality. Case studies suggest that what matters for conflict is a concept closely linked to both economic and ethnic polarization: `horizontal inequalities', or inequalities that coincide with identity-based cleavages. Horizontal inequalities may enhance both grievances and group cohesion among the relatively deprived and thus facilitate mobilization for conflict. This article provides a quantitative test of this argument, exploring whether various forms of polarization and horizontal inequalities affect the probability of civil conflict onset across 36 developing countries in the period 1986—2004. National household data from the Demographic and Health Surveys (DHS) are used to construct measures of ethnic, social and economic polarization, as well as vertical and horizontal inequalities along two dimensions: social and economic. The article also introduces a combined measure of ethnic/socio-economic polarization as an alternative to the horizontal inequality measure. Robust results from panel and cross-section analyses show that social polarization and horizontal social inequality are positively related to conflict outbreak. Variables for purely ethnic polarization, inter-individual inequalities and combined ethnic/socio-economic polarization are not significant.

This article provides a theoretical framework that distinguishes between the occurrence of conflict and its severity, and clarifies the role of polarization and fractionalization in each of these cases. The analysis helps in ordering the various definitions, and in providing explanations for the empirical observations on the relationship between conflict, on the one hand, and polarization or fractionalization, on the other. The behaviour of players in conflict is described as a game, and equilibrium payoffs to all players are computed. The status quo is characterized by a set of political institutions that channel the different opposing interests and turn them into a collective decision, with a second set of payoffs. Groups rebel against the status quo political institution whenever the latter set of payoffs is dominated by the former. When society is highly polarized, the potential cost of rebellion is extremely high, and this cost may serve as the guarantor of peace. So, in highly polarized societies, the occurrence of open conflict should be rare but its intensity very severe, whenever it happens. On the other hand, highly fractionalized societies are prone to the occurrence of conflict, but its intensity will be moderate. It matters, therefore, whether one studies the intensity of conflict, conditional on conflict breaking out, or the likelihood that conflict actually occurs. Specifically, it is shown that: (i) measures of fractionalization and polarization tend to run in opposite directions, (ii) the onset of conflict critically depends on the political system in place, (iii) the occurrence of conflict and the intensity of conflict also tend to move in opposite directions, (iv) the relationship between polarization or fractionalization and conflict is non-monotonic and (v) the intensity of conflict depends positively on the degree of polarization.

One controversy in the study of civil war relates to the role that institutions play in ethnically diverse societies. `Constitutional engineers' advance various institutional arrangements, ranging from democracy in general to specific constitutional and electoral rules, as those mechanisms that help divided societies to resolve disputes peacefully. Political sociologists, by contrast, maintain that political institutions are largely an epiphenomenon. Synthesizing the two conflicting schools of thought, the authors examine how different institutions in conjunction with three forms of ethnic diversity — fractionalization, dominance and polarization — affect the risk of civil war. It is argued that groups perceive institutions as a constraint and that they consider the usage of political violence if they cannot achieve their goals peacefully. The examination of these conditional institutionalist hypotheses for the period between 1950 and 2000 shows, in accordance with recent theoretical work, that fractionalization can indeed be linked to low-intensity civil wars and that this effect is particularly strong in democracies in comparison to autocracies. Interacting the measures of diversity with different democratic institutions, the authors confirm that rules that encourage power-sharing lower the risk of war in diverse societies. The event-history models, moreover, show that the combination of fractionalization and majoritarian voting forebodes badly for the internal stability of a state. Within the set of democratic regimes studied in this article, presidential systems are the most war-prone institutional setting.

Societies are sometimes divided into groups that behave in different ways or have strongly opposing opinions. At other times, everyone seems to behave according to similar principles and opinions. It is likely that individual decisions on behavior or opinions are affected by social networks through influence and selection processes. However, the outcomes are not necessarily optimal for the society as a whole. Two types of problems might arise: (a) polarization of the society into two camps that do not reach consensus, possibly leading to conflict; (b) actors choosing suboptimal behavior, because changing behavior is too risky if done unilaterally. Simulations show that if a society is rather segregated initially, there exists a heightened probability that this situation will worsen. The effect of network density is twofold. First, density has a positive effect on reaching a uniform opinion and, therefore, decreases the likelihood of polarization. Second, density increases the likelihood that actors do not change their behavior, worsening the inefficiency of already suboptimal initial situations.

The ability of political systems to adopt policy reforms contributes to their internal stability. This article analyses 29 anti-corruption reforms in seven sub-Saharan countries. It seeks to explain the level of adopted reform in these countries from conflicts of interests between policy actors. Two groups of policy actors are distinguished: veto-players (endowed with an exercisable veto) and stakeholders (with an interest in policy reforms). A veto-player model is applied and extended with effects of (a) policy polarization between all policy actors and (b) institutional fractionalization between veto-players and stakeholders. The authors hypothesize a negative (interaction) effect of these variables with the win-set on the level of reform. As expected, the core variable of the veto-player model, size of the win-set of the status quo, significantly and positively affects the level of adopted reform. Unexpectedly, the number of veto-players has a significant and positive effect on the level of reform, whereas polarization among veto-players does not affect the level of reform. In contrast, fractionalization between veto-players and stakeholders has a significant negative direct effect on the level of anti-corruption reform and a weak interaction effect with size of the win-set. Thus, even when veto-players agree on the desirability of anticorruption reforms, the adoption of reforms is obstructed by a high level of fractionalization between veto-players and stakeholders.

Terrorism has been shown to influence domestic politics, for example, by altering the priorities of voters and politicians. This article argues that terrorism has broader political consequences than simply putting national security on the political agenda. In particular, it argues that terrorist activity influences government formation. A number of scholars have noted that the presence of an external threat provides an incentive to overcome internal disagreements, suggesting that larger and more inclusive coalitions should form. Terrorist activity may also influence government survival, as voters hold politicians accountable for failing to provide security. Politicians, in anticipation of terrorist activity, may, therefore, seek to form a more stable coalition. The literature on government survival suggests that the size of the coalition positively affects its durability but that its ideological breadth is expected to have an adverse effect on survival, which is the opposite of the prediction of the theory based on external threat. To test whether terrorism influences coalition formation, the author analyzes coalition formation in 17 (primarily Western European) parliamentary democracies over a 50-year period using data on domestic and transnational terrorism from, respectively, the TWEED dataset and the Terrorism Knowledge Base. The results show that government coalitions are more likely to be surplus coalitions and, consistent with the theory emphasizing government survival, more likely to have a low degree of ideological polarization in periods following terrorist activity.

Esteban & Ray formalize the argument that conflict is likely to be more intense when individuals in a society are divided into two clearly identifiable groups where differences within groups are considerably smaller than differences between groups. They show that such polarization increases conflict, and they introduce a theoretical basis for its quantitative measurement. This article applies Esteban & Ray's (ER) measure of polarization to two international distributions: the world income distribution and the distribution of political systems. The article discusses extensions of the ER measure that render it independent of the number of groups in the system, and investigates empirically whether any of the three types of polarization are associated with conflict in the form of militarized interstate disputes. The results are rather inconclusive, despite the fact that some of the micro-level regularities consistent with the polarization and conflict argument have solid support in previous studies.

Ethnic groups and conflicts often transcend country borders, indicating that notions of relative strength and resolve may also surpass such borders. This study focuses on the association between ethnic polarization and conflict in a widened strategic environment, encapsulating each state that experiences ethnic conflict and its neighboring states, and involving contagion processes. Two claims are presented. First, when a state experiences ethnic conflict, neighboring states that are ethnically polarized are more likely to also experience ethnic conflict. Second, when a group involved in ethnic conflict has a kinship tie to a group in a neighboring state, the latter group is increasingly likely to be inspired to challenge the government and end up in ethnic conflict. This should be especially likely if the group resides in a state characterized by ethnic polarization. To evaluate these claims, this article employs logit regression on a global dataset covering the period from 1989 to 2004. The empirical analysis supports the first claim; polarized states are indeed associated with an increased likelihood of contagion processes. The findings also demonstrate that kinship links make contagion more likely; however, this effect is not conditioned by the level of ethnic polarization. The results are robust to a series of alternative specifications. In conclusion, these findings point to the importance of incorporating a widened strategic setting in the analysis when examining the association between ethnic polarization and civil conflict.