Impact of Slavery on Slave Exporting Nations

It's well established that most poor nations are located in Africa. Here's one possible explanation:

Can part of Africa’s current underdevelopment be explained by its slave trades? To explore this question, I use data from shipping records and historical documents reporting slave ethnicities to construct estimates of the number of slaves exported from each country during Africa’s slave trades. I find a robust negative relationship between the number of slaves exported from a country and current economic performance. To better understand if the relationship is causal, I examine the historical evidence on selection into the slave trades, and use instrumental variables. Together the evidence suggests that the slave trades have had an adverse effect on economic development.