I reported now long ago on the consequences of slavery in Africa, where it is shown that countries where more slaves were taken still have lower levels of development. It is quite amazing that this can have an impact on average income for so long. But what about the receiving end of the slave trade?
Graziella Bertocchi and Arcangelo Dimico look at county data for the US and find that current average incomes are not related to the inflow of slaves. However, income inequality is. Why would that be? It could be because slave could not own land, and this still has an impact today. Or it could be because of discrimination. Or it could be because of persistent differences in human capital.
Now using a panel data set, Bertocchi and Dimico find the last one is the most likely one. The education gap between blacks and whites has never recuperated, and segregation was certainly part of it. But this strongly persistent effect means that affirmative action still has a reason to be.