Have thought about this a little more, I wonder culturally, how different two separate Confederacies would be in the long run. Without the Upper South, does the Deep South really have the demographic weight to keep slavery as an institution for a considerably longer amount of time? The racial makeup in some of those states was nearly split even at time of secession. There's also the fact that the Upper South was basically an open air slave market at the time, selling off slaves by the quite literally hundreds of thousands to the Deep South.
There's also the fact that things like bluegrass music, country music, moonshine, that's all an Upper South phenomenon, so I have a pretty good idea of what the popular culture of a Central Confederacy might wind up being, more or less similar to what it is today, but is it possible that the Deep South might wind up significantly more creolized with an even greater black American influence on its culture than its already significant influence broadly speaking?
That last question depends on wether or not slavery is abolished and there’s societal integration.
If slavery is abolished, but there’s an Apartheid system to the modern day, then you can imagine a very 1920’s culture in the sense that a lot of it will be mocking (or villainizing) caricatures of Black people, as well as a clear and separate distinction between low class “jazz” and high grade "white" music, even more so than IOTL. (Obviously, cultural appropriation will happen, but it’ll be much slower, and will be much more white-washed.)
(Basically, ITTL, Elvis would be considered too progressive in the Deep South, far more than he was IOTL, for popularizing Black music. The Central South would see him as a deity tho.) (Hell, it’s possible that Tennessee moves its capital to Memphis (and turns it into a consolidated city-county) just to bask in the glow of being next to Graceland.)
The North, meanwhile, would most likely be culturally defined by more mocking of the southern states (because they’d most likely become backwaters), as well as there being some jingoism/good riddance sentiments regarding the seceded states. The Plains would become the new South, serving as the rural agricultural region for the country. If relations are good enough for there to be a something of an EU agreement between the countries, then it’s basically OTL, except the North just has a more progressive government, the Central South wobbles between Bill Lee Republicans and Andy Beshear Democrats depending on the election season, and the Deep South, left to its own devices… well, let’s just say their politicians would make Steve Scalise look outright moderate, if not outright progressive. (In the case that there hasn’t been an end to Aprtheid.)
If there has been an end to Apartheid, you basically get the South from OTL, except more conservative/liberal depending on how the Apartheid ended and how open the borders between the countries are.
If the Apartheid ended due to internal reform, and there’s the same border policy as IOTL between the countries as the US has with Mexico, the Deep South is more conservative since there’s no danger of a mass exodus of their Black underclass, and they’ll reform just enough to keep their system going, and to get the inevitable embargoed against them to stop.
If it’s because there was an outright civil war, or just mass armed resistance (most likely funded by the US to screw over the Deep South out of revenge/to keep Black people there fighting rather than emigrating) and there’s an open border between the Deep South Confederacy and the U.S. (meaning that if they fuck around, there will be a mass exodus of Black people), then it’s possible this Deep South looks like what our South would look like if you had both the Wyoming Rule (for greater representation) and explicit requirements for minority-majority congressional districts (even possibly a constitutional requirement for quotas at the government like Rwanda has for women).
