The goal of the paper is to demonstrate how international slave trade spread the institution of slavery throughout Africa, resulting in long-term effects of the continent’s income and political centralization. The author first estimated the travel time to slave ports from each society in the Ethnographic Atlas to determine predicting factors for the adoption of slave trade in African societies. The author reported that societies with high exposure to slave capture in the past were more likely to have the custom of slavery and the custom of polygyny. The author further suggested that slavery institutions emerged in West Africa through local, politically centralized aristocratic systems while emerging in East Africa through the preservation of wealth within the nuclear family over generations.