...succeed from the union...
Secede.
And I don't think there's any question that abolition of slavery was a threat to the cotton-based agrarian economy of the South. The Union had a far wider industrial base, whereas eliminating slavery would cripple the South's economy.
I recall an argument I read that even without the Civil War, the South over several decades would have gradually abandoned slavery. And a separate book I wish I'd purchased, that made a case for the Southern states' absolute Constitutional right to secede, and that the North violated their Constitutional rights in declaring war and taking them back.
