Go read Lincoln’s inaugural address.

The majority is about how he wasn’t going to federally outlaw slavery.

So yeah. The SC was proslavery, but the North wasn’t against it either until well into the war. Even then it wasn’t about doing the right thing. Wealthy Europeans knew the north would win, but also knew Southern landowners would sell on the cheap during the war.

By federally outlawing slavery, it made the agricultural land in the South drop in value.

This allowed the war to end significantly earlier.