What explains differential rates of ethnic violence in postcolonial Africa? I argue that ethnic groups organized as a precolonial state (PCS) exacerbated interethnic tensions in their postcolonial country. Insecure leaders in these countries traded off between inclusive coalitions that risked insider coups and excluding other ethnic groups at the possible expense of outsider rebellions. My main hypotheses posit that PCS groups should associate with coups because their historically rooted advantages often enabled accessing power at the center, whereas other ethnic groups in their countries—given strategic incentives for ethnopolitical exclusion—should fight civil wars more frequently than ethnic groups in countries without a PCS group. Analyzing originally compiled data on precolonial African states provides statistical evidence for these implications about civil wars and coups between independence and 2013 across various model specifications. Strikingly, through 1989, thirty of thirty-two ethnic group-level major civil war onsets occurred in countries with a PCS group.