A classical theme in social analysis views economic class divisions as the main cause of social conflict. Yet many, if not most of the conflicts we observe today appear to be ethnic in nature. It appears that the "vertical" nature of class divisions is often dominated by the "horizontal" antagonisms across groups delineated by noneconomic markers. This paper highlights the perverse synergy of economic inequality within ethnic groups, and its role in the salience of ethnic conflict. In a model of group formation which allows both class and ethnic groupings to emerge, we show that ethnic, as opposed to class, conflict may be focal, and precisely in the presence of economic inequality.

This paper describes how wealth inequality may distort public resource allocation. A government seeks to allocate limited resources to productive sectors, but sectoral productivity is privately known by agents with vested interests in those sectors. They lobby the government for preferential treatment. The government—even if it honestly seeks to maximize economic efficiency—may be confounded by the possibility that both high wealth and true economic desirability create loud lobbies. Broadly speaking, both poorer economies and unequal economies display greater public misallocation. The paper warns against the conventional wisdom that this is so because such governments are more “corrupt.”

We develop the measurement theory of polarization for the case in which income distributions can be described using density functions. The main theorem uniquely characterizes a class of polarization measures that fits into what we call the “identity-alienation” framework, and simultanously satisfies a set of axioms. Second, we provide sample estimators of population polarization indices that can be used to compare polarization across time or entities. Distribution-free statistical inference results are also used in order to ensure that the orderings of polarization across entities are not simply due to sampling noise. An illustration of the use of these tools using data from 21 countries shows that polarization and inequality orderings can often differ in practice.

We examine empirically the impact of ethnic divisions on conflict, by using a specification based on Esteban and Ray (2011). That theory links conflict intensity to three indices of ethnic distribution: polarization, fractionalization, and the Gini-Greenberg index. The empirical analysis verifies that these distributional measures are significant correlates of conflict. These effects persist as we introduce country-specific measures of group cohesion and of the importance of public goods, and combine them with the distributional measures exactly as described by the theory.

We provide a model of conflict and mass killing decisions to identify the key variables and situations that make mass killings more likely to occur. We predict that mass killings are most likely in countries with large amounts of natural resource rents, polarization, institutional constraints regarding rent sharing, and low productivity of labor. The role of resources such as oil, gas, and diamonds and other key determinants of mass killings is confirmed by our empirical results based on country-level as well as ethnic group–level analysis.