As evidence, here is a review of some of the economic literature on the effects of the slave trade on "sending" African countries.

A new research line initiated by Nunn (2008a) has instead concentrated on the effects of the slave trades. Nunn (2008a) presents a systematic empirical analysis of the effects of the slave trades on current economic performance. His first contribution is a database reporting estimates of the number of slaves exported from each contemporary African country in each century from 1400 to 1900. The estimates, which are based on shipping records, including the Trans-Atlantic Slave Trade Database (Eltis et al., 1999) and a variety of historical sources, also report the ethnic identity of slaves. The second contribution is to show a robust negative relationship between the number of slaves exported from a country and per capita income in 2000, despite evidence that the slave trades were more intense in the most developed and most densely populated areas in Africa. Through two-stage least-square estimation (where the sailing distances from each country to the nearest locations of demand for slaves are employed as instruments), he can also establish that this relationship is causal. Moreover, he suggests that the channels behind the observed relationship have to be found in the fact that the slave trades impeded the formation of broader ethnic identities, by stopping the homogenization of ethnic differences, thus leading to fractionalization and weak and fragmented political structures. The impact of the slave trade on ethnic stratification has also been studied by Whatley and Gillezeau (2011), who establish the existence of a positive relationship between current ethnic fragmentation and slave exports from West Africa.