A lot depends on how badly damaged the Union states are in the war.
Assuming that the USA loses and the CSA wins with the help of France and the UK. UK and France may want tariff-free access to US markets as part of the peace treaty.
The remaining USA states lose the revenue of export of the cash crops for the southern states like cotton, tobacco, indigo, rice, and naval stores.
A lot depends on how well the USA adapts to being much smaller and being seen as weaker than the empires of Europe.
Long-term a much smaller USA staying out of WWI might be the biggest butterfly from an independent CSA.
Note that all of the fightings were far away from Union’s industrial centers. Plus, while those commodity exports were nice, exports as a whole long accounted for like 6-7% of US GDP by 1860 and the US actually ran a trade deficit for most of the pre-Civil War period. In the end, it was mainly a domestic-driven economy.
The US had all the manpower, skills, tools and resources to adapt to new circumstances.
Also, France would not be capable of enforcing anything on the US.
Generally, it's uncompetetive politics that favour certain regions over others that drive secessionist sentiment, not the other way around.
Unless that politics is uniformly supported by like 20 out of 23 states. Secession only happens when the minority is strong enough to do so, you know, like the Confederate, and/or receives support from another great power.
After airconditioning becomes an option and the Rust Belt starts to depopulate with people moving to the Sun Belt in the second half of the 20th century the USA could go into population decline.
Not going to happen. The movements from the North to the South were internal migration, not emigration. You would never ever have mass emigration from the US.
I don't see why both can't occur at the same time? I mean, even if the aristocratic class makes that claim towards the creation of a Labor movement, I don't see that as being different than what many nations in the Americas and Europe acted towards growing Labor movements and really if inequality still rises, it probably does get attempted and gain some level of traction after some difficulty
Don’t forget that loads of oppressed white Unionists and poor whites would leave for the North. Meanwhile, the Great Migration of African Americans would have been butterflied away. The Confederate would move towards South Africa/Rhodesia in terms of politics and society.
Now I do believe places like Texas would grow a population due to Oil and Land (I do think even with the slave focus economy of the CSA, there would be a drive for people to move there)
The OTL migrations to Texas were largely internal migrations from other parts of the US. ITTL, that would have been severely curtailed. Immigration is an entirely different beast from internal migration.