Okay, so I've been thinking about this and now I'm kinda stumped on a few bits.
I've got a rough idea of what exactly happens to form a confederate states that's primarily run by african americans, but apart from the basics timeline: Confederates win pyrrhic victory then black slaves revolt while white masters are weak, I'm unsure about other things.
For instance, would the Union support it? (I doubt so but the US has a habit of supporting regime changes all the way from Hawaii and Mexican owned California)
Would there be white flight, and to what extent? Would it be like Zimbabwe? Would states secede from the confederacy to the union?
Depends on the outcome. Certainly, I don't think even the most powerful plausible revolt would have any chance of actually overthrowing the C.S. in
peacetime.....but if there's been another war, especially if circa say, 1890 or later, I can certainly see the Union being all too happy to oblige in assisting the rebellious slaves, and should the Union win.....well, it would seem to be dependent on how the political situation in the Union is in regards to reunification. If the desire for such remains strong, then these now former slaves will at least receive full U.S. citizenship and, in addition, one possible scenario emerges afterwards; in exchange for laying down their arms, they are given a choice of either settling on confiscated planters' lands, or they may leave the occupied south and move elsewhere, to any location were housing is available(of course, a fair few reactionary types would likely try to cause trouble, sadly, but then again, that's what the state National Guard units would be for; keeping the peace at home. And with attitudes amongst most of the rest of America opposed to all that the Confederacy stood for, strongly so in some cases, there would not be any real tolerance for such shenanigans.). There is also, for those that can, the option to immigrate to Liberia.....
But if it's not as strong.....then it is quite possible, at least, even fairly plausible under the right circumstances, that a rump state may indeed be set up for freed African-Americans post-war.(One possible scenario might involve large parts of MS & AL, and perhaps even much if not all of the Florida Panhandle, being annexed, and maybe even a few other bits added on, like the Florida Parishes in LA). That said, though, for those who'd rather not be part of a new country, they can always move around the U.S, or even go to Liberia if possible, as in the other scenario.....