Inequality and conflict are inextricably linked. A considerable amount of research has been done attempting to understand the links between the two. Both vertical (between households or individuals) and horizontal inequality (between groups) as well as perceived inequality have been examined. In this report, we review and synthesize the large literature on inequality and conflict and perform a mapping exercise for data on vertical, horizontal, and perceived inequality. We show that while vertical (economic) inequality is at an all-time high, horizontal inequality has declined steadily throughout the world over the past 25-30 years. Indeed, in sharp contrast to vertical inequality, horizontal inequality is at the lowest levels on record.
Vertical and horizontal inequality, and armed conflict
The conventional wisdom holds that inequality triggers conflict and violence. Initially the literature focused primarily on vertical inequality. However, the inability to explain how and why inequality mobilizes certain groups for violence has plagued the existing literature. Theories of horizontal inequality are better placed to address this question and there is an increasing convergence around the conclusion that horizontal inequality is associated with armed conflict. That said, several gaps are still evident in this literature. First, while the evidence is strong of a positive relationship between horizontal inequality and violent armed conflict, and that political context plays an important role in this relationship, the conditions under which certain group identities become relevant for mobilizing people for violence is still unclear. Second, any interactions between different types of horizontal inequality, as well as interactions between within-group and betweengroup inequality, are under-studied. Third, studies have found a relationship between horizontal inequality and various forms of political violence, but also non-violence. We currently lack an understanding of the factors that explain why groups choose violent versus non-violent strategies.
Finally, we still do not know enough about the differences between distinct types of horizontal inequality – social, political, and economic – or the relative importance of different types of group identities such as ethnicity, religion, age, gender.
Perceived inequalities and conflict
Prominent authors within the horizontal inequality literature (Stewart 2000, 2002 Cederman et al. 2013) have emphasized the central importance of how inequality is experienced, or perceived. This topic remains woefully understudied empirically, although the few studies that exist indicate that perceived inequality and violence are clearly linked. Furthermore, perceived and objectives horizontal inequality do not necessarily overlap. Indeed, we show that the correlation between the two is quite low. The relationship between perceived horizontal inequality and attitudes to violent conflict is thus not an artifact or proxy for the relationship found between objective horizontal inequality and conflict. More and better quality data to measure perceived inequality, as well as a deeper knowledge about how these perceptions are triggered, are crucial for assessing more fully how inequalities affects conflict. Large standardized surveys like AfroBarometer should be supported so they can continue to collect perceptions data, but we also need to invest in new approaches to measure perceptions, such as those developed through the Governance, Peace, and Security modules of the Strategy for the Harmonization of Statistics in Africa (ShaSA) initiative.
How to address inequality
Given that objective and perceived inequality are abound, what can be done to address exclusion and manage conflict? Available evidence suggests that political institutional arrangements, such as territorial decentralization, educational policies, and cultural recognition can help to avert that armed conflicts break out. Moreover, some aspects of political and military power-sharing as well as territorial autonomy seem to reduce the risk that violent conflicts recur. Post-conflict educational provision has been shown to positively impact peace duration, while post-conflict economic policies have a more mixed record. Peace agreements often address grievances believed to be driving violent conflicts. However, few agreements make specific provisions aimed at addressing key economic issues like systematic inequalities in employment and access to land.
The evidence base for the effectiveness of policies adopted to address horizontal inequalities on conflict onset and recurrence is very limited, and there is a need for much more rigorous analysis of policy outcomes. Future research needs to pay particular attention to improving our understanding of the sequencing of reforms; to how and why context matters; to interaction and conditional effects; to the ways in which policy or economic reforms can trigger conflict; and to how such reforms may again shape perceptions of inequalities.
Trends in inequality – rising economic and falling horizontal inequality
The answer to the question of whether income inequality in the world has increased or declined depends on how inequality is both operationalized and measured. In this report, we provide an overview of different approaches to measuring both individual and group-based inequality, focusing in particular on how survey data can be used to construct globally comparable measures of horizontal inequality. For global economic vertical inequality, our mapping shows indeed that the world has not seen a level of inequality this high for as long as we have reliable crossnationally comparable data. This is shown in Figure 1. Global inequality, as measured by the average national Gini coefficient (red line), gradually decreased from 1960 to 1990, then increased back to the 1960 level in the mid-1990s and hovered around or above that level for the next twenty years. The difference between the population-weighted and the unweighted time series indicates that increasing inequality is most pronounced in the largest countries in the world.