> The American South, where slavery was more prevalent, is poorer than the North.

Does this analysis account for the fate of the former slaves and their descendants? I think part of the "wealth" of a society built on these things is leaving those effects as an externality. That doesn't really work when the people who were oppressed are freed and live among you.

European nations who strip mined the rest of the world never really had to account for this head-on, since the most visible exploitation was safely far away.