cementing the south's slowed economic development after the war.

https://en.wikipedia.org/wiki/Human_capital_flight

Research shows that there are significant economic benefits of human capital flight for the migrants themselves and for the receiving country. The impact on the country of origin is less straightforward, with research suggesting the impact can be positive, negative or mixed. Research also suggests that emigration, remittances and return migration can have a positive impact on democratization and on the quality of political institutions in the country of origin.

When you make a geographic area unwelcome to a people while opening up different ones, don't be surprised if that area has problems and the others prosper.