It wasn’t even about states rights, not really. If you read the SC declaration of succession, they talk extensively about the states rights to succeed legally and why in the first 13 paragraphs, then in the 14th they start the explanation of why they are succeeding. It’s about the northern states not returning fugitive slaves, as was the law at the time, and the government doing anything to enforce the Constitution. Then in paragraph 22 they discuss the election of Lincoln and his open opposition to slavery and they were worried about losing the right to have slaves.
Basically, if the government isn’t strong enough or willingly to enforce its own constitution, then they didn’t need to be a part of that government and they had the right to denounce that government the same way they had done with the British government during the revolution.
It’s 100% about slavery and there isn’t
It was absolutely about states’ rights.
… to keep the institution of slavery alive.