States Rights - the south went to war over the issue of the centralized government (feds) wanting to lord it over them. slavery was a secondary issue. The average everyday southern had no slaves. The average Confederate Soldier was not fighting for the blacks, but for a way of life that they only knew.
So how was the centralized government lording it over the southern states?
Righto. Sadly, that way of life was based on slavery, as they themselves repeatedly said.
Feel free to point out exactly how the central government was lording it over the South in 1860.
In actual fact, southern Democrats walked out of the Democratic Party convention in 1860 (twice) over refusal of northern Democrats to bow to their demand for a federal Slave Code imposing slavery in every territory, regardless of whether the inhabitants wanted it or not.
So there is actually a better case that the South seceded because they didn’t get the expansion of federal power they wanted.