We know that the southern states seceded due to slavery due to slavery. We know that to be fact as that is what those states told us in their Declarations of Secession.
It is all right there in that documentation for the entire world to read.
And if it were about states’ rights, they would have mentioned states’ rights in those declarations, but instead they only mention slavery.
The facts are the facts and no matter how hard the Confederate Apologists try, they cannot erase the facts of the reason the south left the Union.
The South Carolina declaration accuses the north of breaking the constitutional compact by refusing to return fugitive slaves. That actually is a constitutional requirement and the northern states actually did break it. The declaration attempts to assign blame for the breakup using the language of the original compact. They couldn't claim state's rights since at the time those were not in question. They couldn't claim an unfair tariff since the constitution allows tariffs and does not limit them. They couldn't claim anything about the disposition of the western territories since the constitution is silent about such matters. But the fugitive slave clause was a smoking gun and that is what they argued.
AR,TN,NC and VA seceded over the issue of Union Usurpation. That is fact.