They were trying to enforce slave owner “property” rights prior to seceding, through passing federal laws like the fugitive slave act, that northern states were doing their best to avoid cooperating with. In their letters of secession, they complained that according to the constitution and federal laws, the northern states should have been forced into recognizing slave owner “property” rights. They go on to state that the northern states not complying with federal laws has nullified the constitution, so they’re effectively their own country now, deal with it. To paraphrase.
The General Government, as the common agent, passed laws to carry into effect these stipulations of the States. For many years these laws were executed. But an increasing hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, and the laws of the General Government have ceased to effect the objects of the Constitution.
A geographical has been drawn across the Union, and all the States north of that line have united in the election of a man to the high office of the President of the United States, whose opinions and purposes are hostile to slavery
Things like tariffs or taxes that some people bring up aren’t even really mentioned in the letter. And it’s quite long, so they had plenty of space. Goes on and on for a while about why they should be able to secede, and then just dives into not only their “property” rights to hold slaves and that they should be able to enforce slave laws in Northern states too.
“property” always in quotes in my comments here, because of course in these letters they are always abhorently referring to people as property.
Here they go on and on again about their grievances with each northern state, and how they believe this releases them from the union:
The State of New Jersey, at an early day, passed a law in conformity with her constitutional obligation; but the current of anti-slavery feeling has led her more recently to enact laws which render inoperative the remedies provided by her own law and by the laws of Congress. In the State of New York even the right of transit for a slave has been denied by her tribunals; and the States of Ohio and Iowa have refused to surrender to justice fugitives charged with murder, and with inciting servile insurrection in the State of Virginia. Thus the constituted compact has been deliberately broken and disregarded by the non-slaveholding States, and the consequence follows that South Carolina is released from her obligation.
Notice the grievances are all about former slaves not being extradited back to southern states of course, or about other states not recognizing people as property. But to answer your question, I’m not saying South Carolina thought leaving the union would improve its control over Northern states, that wouldn’t make a ton of sense, but that is what they were trying to do prior to leaving though. Maybe they thought they’d be able to have stricter flow of people or better bargaining position with northern states as an independent country. I’m pointing all this out because they didn’t leave because of some sort of idealogical stance about “state’s rights” as some people say. It was all about slavery. And they had no problem pushing to trample states’ rights when it came to slave laws, including in their own constitution they eventually wrote for the confederacy.
MxM111