Civil War did not start over slavery, it started over Fort Sumter.
But slavery soon became an issue during the war, as first thousands, then tens and hundreds of thousands of slaves escaped to Union Army lines.
By law they could be declared "contraband" and freed, and so they were.
Slavery could only be abolished nationwide by constitutional amendment, and so it was, in 1865.
Of course you know all that, but continue to lie about it anyway.
Too bad.
It started because both the Federal Government and the New York centric power barons were both going to lose a hell of a lot of money. Ft. Sumter was a pawn.
They didn't care about the slaves. They cared about the money and the power it gave them.