In a nutshell:
All four of them. Or was it only three? I forget. I know it wasn't all 11 states, but in our modern discussions of this, it has become common place to accept that this minority of states represents the majority. Dishonest, that.
Civil war started not over slavery but over Federal properties and restoring the Union.
"Federal Properties" is just the token excuse. Fort Sumter was useless, and never served the nation's interest in any fashion other than as an excuse to start a war with people cutting the money stream to New York and Washington. Fort Sumter was only manned for a very short time after the war, only to maintain the pretense that it had some kind of value or importance to the USA. Eventually they realized it was no longer worth the trouble to keep up the pretense, and so they just stopped, and it has been basically abandoned ever since.
"Federal Properties" my @$$. It always was just an excuse.
Today's Lost Cause mythologizers just can't get over slavery, secession, rebellion, emancipation, abolition & full citizenship so they spend endless hours caterwauling cockamamie cognitive confusion about "power & money" over tariffs & "unfair spending".
And here is where you just smear people because they are whipping your @$$ in the raw facts of the debate. I don't give a sh*t about full citizenship for freed slaves, and I contend that was going to eventually happen anyways. What bothers me is the fact that some Plutocracy that is still running Washington DC today, launched a war over money that killed 750,000 people directly, possibly another 2 million indirectly, destroyed the relationship between the States and the Federal government which the Founders had established, and created the gargantuan borrow and spend monster that is currently eating us alive today.
You want to keep the topic on slavery, because it is the only possible way to pretend the civil war was not a horrible disaster, which it was, and it is also the only moral justification of which anyone can think for what was done. The problem is, it's just wrong. It isn't supported by the facts, and the Corwin amendment alone should make that clear to any objective person.