The confederacy wanted more state rights and was sick of the Northern part of the country pushing them around. Slavery was the final straw. With the mass production going on in the south they needed slaves to keep up with demand that they have built for years.

The Civil War was not 100% about slaves. In today's world ignorant people just keep acting like the Civil War was all about slaves and the confederacies right to own slaves. By their logic the American Revolution was solely about guns because the British coming over and trying to take away the guns was the final straw. The American Revolution was more than just about guns.

Even if the confederacies successfully broke free from the Union slavery would have naturally died out due to the invention of Tractors and other easier methods to farm.

Also people ignore how mainly the rich elites had slaves. The rich people being the plantation owners. Average people like you and me couldn't afford slaves nor afford to keep them alive.