This research advances the hypothesis and establishes empirically that interpersonal population diversity, rather than fractionalization or polarization across ethnic groups, has been pivotal to the emergence, prevalence, recurrence, and severity of intrasocietal conflicts. Exploiting an exogenous source of variations in population diversity across nations and ethnic groups, as determined predominantly during the exodus of humans from Africa tens of thousands of years ago, the study demonstrates that population diversity, and its impact on the degree of diversity within ethnic groups, has contributed significantly to the risk and intensity of historical and contemporary civil conflicts. The findings arguably reflect the contribution of population diversity to the non‐cohesiveness of society, as reflected partly in the prevalence of mistrust, the divergence in preferences for public goods and redistributive policies, and the degree of fractionalization and polarization across ethnic, linguistic, and religious groups.

This research advances the hypothesis and establishes empirically that interpersonal population diversity has contributed significantly to the emergence, prevalence, recurrence, and severity of intrasocietal conflicts. Exploiting an exogenous source of variations in population diversity across nations and ethnic groups, it demonstrates that population diversity, as determined predominantly during the exodus of humans from Africa tens of thousands of years ago, has contributed significantly to the risk and intensity of historical and contemporary internal conflicts, accounting for the confounding effects of geographical, institutional, and cultural characteristics, as well as for the level of economic development. These findings arguably reflect the adverse effect of population diversity on interpersonal trust, its contribution to divergence in preferences for public goods and redistributive policies, and its impact on the degree of fractionalization and polarization across ethnic, linguistic, and religious groups.

Diversionary war theory holds that insecure leaders are more likely to pursue aggressive foreign policies than their more secure counterparts. This hypothesis rests on the premise that interstate dispute involvement helps leaders deter potential challenges against their rule. We offer strong support for this premise by looking at coup attempts. Cross-national time-series evidence from interstate dispute participation over the period 1960–2000 indicates that a country in a militarized confrontation with another state is about 60% less likely to experience a coup attempt in the subsequent year. Consistent with our hypothesis, we establish that it is mainly militarized involvement in disputes, rather than non-militarized involvement, that is associated with lower coup likelihood. The results are robust to controlling for a wide set of potential correlates of coups and remain qualitatively intact when we focus entirely on within-country variations in coup attempts and interstate disputes.

This research establishes that the emergence, prevalence, recurrence, and severity of intrastate conflicts in the modern era reflect the long shadow of prehistory. Exploiting variations across national populations, it demonstrates that genetic diversity, as determined predominantly during the exodus of humans from Africa tens of thousands of years ago, has contributed significantly to the frequency, incidence, and onset of both overall and ethnic civil conflict over the last half-century, accounting for a large set of geographical and institutional correlates of conflict, as well as measures of economic development. Furthermore, the analysis establishes the significant contribution of genetic diversity to the intensity of social unrest and to the incidence of intragroup factional conflict. These findings arguably reflect the contribution of genetic diversity to the degree of fractionalization and polarization across ethnic, linguistic, and religious groups in the national population; the adverse influence of genetic diversity on interpersonal trust and cooperation; the contribution of genetic diversity to divergence in preferences for public goods and redistributive policies; and the potential impact of genetic diversity on economic inequality within a society.

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