How are ethnic inequality and ethnic violence related? We empirically investigate this question using an innovative measure of resource inequality between ethnic groups, based on rainfall on ethnic homelands during the plant-growing season. Our main dataset covers the period 1950–2020 and includes 250 ethnicities, located across 43 African countries. Our results indicate that rainfall-based inequality is a strong predictor of ethnic violence and that the link heavily depends on the power relations across ethnic groups. In terms of mechanisms, our results suggest that resource inequality leads to more ethnic conflicts by exacerbating grievances.