They why did the confederate state’s formal declarations of succession say that slavery was the reason they were succeeding?

It was explicitly NOT about states' rights. The Confederacy hated states' rights. They were the ones pissed they couldn't enforce their shitty laws in the North. They prevented any of their member states from ever outlawing slavery.

That line isn't just a cutesy way of hiding the ugly part behind the technical truth, it's a flat out lie.

Technically it was over a state's rights to ban slavery.

The slavers really hated that and wanted to expand as much as possible.

Remember when Republicans did shit recently in the name of "state's rights" to hate and then when states that didn't want Trump's bulashit said "oh let's pass our own laws to undo his cuntery" Republicans and Trump said these states had to follow federal law?

Ra damn Trump and Republicans are hypocrites.

Article I Section 9(4) of the Confederate constitution:

No bill of attainder, ex post facto law, or law denying or impairing the right of property in negro slaves shall be passed.

Yeah, they specifically restricted state's rights.

B̵̃ͅ ̷̰̆U̵͇̾ ̷̪͝Ṟ̶͛ ̴̙͋Ṇ̷̌

States' rights to do what, motherducker!