# **1 Introduction**

This paper addresses the interplay between socioeconomic and identity-related factors in civil conflict, guided by a comprehensive approach to organized group conflict, which has been brought to the fore by Stewart (2000; 2002) as the concept of horizontal inequalities (HIs).<sup>1</sup> In brief, the argument is that inequalities that coincide with identity cleavages (such as ethnicity, religion or regional affiliation) may enhance group grievances and thus facilitate mobilization for conflict. In a series of case studies Stewart (2002) found that various dimensions of HIs provoked some kind of conflict, ranging from a high level of criminality in Brazil to civil war in Uganda and Sri Lanka. In order to test whether these findings can be generalized beyond the particular case studies there is a need for large-N investigations. Drawing on national survey data, Østby (2005a) has provided quantitative evidence that Stewart’s findings hold when socioeconomic inequalities between ethnic groups are tested systematically across 33 developing countries. She also found similar effects for horizontal inequalities at the regional level with a much larger sample (Østby, 2005b), whereas Brown (2005) reports statistical evidence for a positive effect on conflict of horizontal inequalities between religious groups.

An important issue that has not been systematically addressed to date is whether horizontal inequalities are especially conflict-provoking under certain political conditions. To my knowledge, there has been little systematic theorization of the role of political institutions (such as regime type, and electoral system) in ameliorating (or exacerbating) the conflict potential of horizontal inequalities. This paper examines the independent and interactive effects of socioeconomic horizontal inequalities and regime type, electoral system, as well as actual political exclusion of minority groups. I put forth specific hypotheses as to how the political environment interacts with socioeconomic horizontal inequalities. For instance, I expect that horizontal inequalities may be particularly explosive in democratic and semi-democratic regimes because the relatively deprived groups have both a strong motive and the opportunity for violent mobilization. In order to test these hypotheses I conduct a large-N analysis of civil conflict in up to 55<sup>2</sup> developing countries in the period 1986–2003.

The paper is organized as follows: Section 2 provides a theoretical framework for the relationship between horizontal inequalities and conflict, with a special focus on three different group identifiers: ethnicity, religion, and regional affinity. Section 3 discusses the possible impact of regime type, electoral system, and political exclusion of minority groups in mitigating 1 Horizontal inequality should be distinguished from ‘vertical’ inequality, which measures inequality between individuals in a society, regardless of ethnic affiliation or other group characteristics of the population. Recent large-N contributions of civil war (e.g Collier & Hoeffler, 2004; Fearon & Laitin, 2003) tend to dismiss inequality as a grievance factor, based on such a vertical measure of inequality, hence ignoring the impact of HIs.

2 Although the DHS surveys allow me to calculate HIs for 61 countries, 6 of these disappeared from the regression analysis either because there was a conflict going on during the entire period 1986–2003 implying that all conflict years were deleted, or due to missing observations on certain of the other variables in the analysis for the entire period 1986-2003 (India; Myanmar; Liberia; Philippines; Sudan and Turkey) 4