Um, as history tells us, the South fired the first shots of the Civil War at Fort Sumter. Therefore, the South (or more correctly, South Carolina) began the war with the United States. And they did not peacefully secede, they forcibly took over all forts and arsenals in the South after they seceded.
And the war was over slavery. The federal government stopped the expansion of slavery, so Southern states felt this was a blow to their rights as states. So they seceded, starting with South Carolina.
And the war was over slavery. The federal government stopped the expansion of slavery, so Southern states felt this was a blow to their rights as states. So they seceded, starting with South Carolina.