Can Africa's poverty today be traced in part to the slave trades? Nunn builds the evidence needed to test the proposition, drawing on shipping records and on historical documents that identify the ethnicities of enslaved people to estimate how many were taken from each African country.

Matched against present economic performance, those estimates yield a consistent negative relationship: the countries that lost the most people are the poorer ones now. Showing that the pattern is causal rather than coincidental takes further work, and Nunn examines the historical evidence on which societies were drawn into the trades in the first place, alongside estimates using instrumental variables. Taken together, the results indicate that the trades damaged later economic development.