The South never cared about States’ Rights. One of their grievances was that Non Slave States would not hold and return escaped slaves and would not recognize any authority for slave capture agents (read that as gangs).

The simple reality is that slavery gave some landowners in the south, especially the Deep South, outsized political power but it was hampered by not being able to expand it with new states in the West.

It has been argued as well that slavery actually cost the Confederacy the war to some degree. Mississippi, Alabama and Georgia didn’t really have the population of free landowners needed to raise significant forces, that’s why Virginia is so outsized in the history of the conflict, it had a relatively small slave population but a very large citizenry who ended up being on the actual front lines due to geography.

If anything, the Executive Authority of the Confederacy was as much an issue as what Lincoln did. Currency manipulations, forced conscriptions of men who never had a stake in slavery as an institution and permitting the abuse of land seizures of veterans who fell in battle if they didn’t have male children old enough to own land, which was also about the time they could be conscripted.

Executive Power expands because the rest of the political class allows it. It’s easier to let a President eat the blame for failures while term limits allow the legislature to effectively claim credit for successes after the fact. PAC money and Dark Money actually accelerate this dynamic as it’s much more comfortable getting paid off to let the Executive branch overreach.

The Confederacy would have been worse if it had survived. Not that it was likely to have been relevant fifty years on.

Slavery was already showing its economic and cultural weaknesses in civilizational comparisons when the war broke out. The Confederacy just illustrated how slavery was also a political weakness as well.