A lot of communists like W.E.B. Dubois dedicated a good amount of research to the 2nd phase of reconstruction after the US civil war, often called the counter-revolutionary phase, where a lot of the gains of the civil war were lost.

Their belief is that slavery was allowed to be reinstituted in a limited form in the south (mainly in prisons), black leaders removed from their posts and replaced by confederates, white terrorist orgs like the KKK reformed and turned a blind eye to, and the harsh enforcement of miscegenation laws (many of which only got repealed in the 1960s).

That campaign of terror is what drove black mass migration out of the south and into the US west coast, and north throughout the 20th century.

Obviously the US hasn't really changed that policy, and still lets the south have slavery in limited forms.

The books black reconstruction, and michelle alexander's the new jim crow are great ones abt this.