I forgot another alternate history path I had intended as a way, actually the way, to spawn the Central Confederacy.
If the US is doing badly enough far enough in the War then you get the Peace Democrats event.
This forces a decision to either make peace or establish a Republican dictatorship.
But the dictatorship immediately triggers a Central Confederate uprising.
It's basically a last-ditch effort by a Union that has decided that it is worth gambling on losing EVERYTHING but New England for a shot at not losing the Southern States. A Union that is losing the War, but it is willing to broaden the scope of the War even more if it believes it can salvage it.
Aside from running out the clock (and that does require winning, ie, outperforming the historical Confederacy), the Trent Affair can fire if Anglo-American relations are sufficiently bad, or perhaps make it a little more generalizable to any large industrial country.
It DOES NOT cause a British entry into the Civil War on the Confederacy's side. Britain may have armed them but they more or less hated them. It just starts a second, separate war with something like a "cut down to arms" casus belli. So Britain isn't an ally to have fight your war, it's another distraction (open another war of limited scope).
I think an interesting idea that could either be done by paradox or modders (because it may or may not be controversial) would be to partition the South in multiples ways with Greco-Turkish style population transfers to create majority African states that could be given be autonomy or even independence. I don't know if the government would have had the political power/ capital to do this IRL but perhaps in the game if you strengthen the government it could be an option.
That's a very good idea and close to what I think should have been done IRL. (Yes, Black Amerika would have been a dysfunctional hellhole, but it's their hole to hell if they want.)
IRL I think you'd have to have somebody like William Seward in charge.
Something Victoria does not represent, even though it's actually more important to this timeframe than any other besides Crusader Kings, is a model of federalism. The closest it gets is the slave laws being state-by-state, and that solely to make the US functional. I've thought about different possibilities before, but it's a hard question no matter what. New Afrika could be something like a vassal. Federalism could be used, among other things, to have different culture laws in different places.
I've also thought about the possibility of Confederate-Liberian relations. Liberia had adopted this hypocritical system of forced labor, didn't call it slavery but it was de facto slavery and they were, of course, culturally very similar with antebellum architecture, fashion, customs and such. The Liberians gave the impression of still thinking of themselves as Southern in some fashion, named their cities after Southern states. I've wondered if a successful CSA sending Liberia its freedmen (something the Fire Eaters always hated having around) could have actually steered Liberia to becoming an explicit slave society and a partner in African colonization. When I've played CSA in Victoria II i've always made Liberia my top diplomatic priority and I'd use the console commands to feed it what I colonized.
P.S. It would be sick if the Hunley was in the game somehow, even just as a harbor defense weapon (which is what it for all purposes was). Balloon corps is also cool, though that's really just basically a tech (+ to recon or whatever).