For what purpose might people form a confederacy?

The purpose of forming the Confederacy was the fact that the North wanted change. Since the South had slaves and that was their lifestyle they thought it was trying to get taken away from them. Slaves were the highest income for the south. With this being said, if you lived in the south and had slaves who made you lots of money, you wouldnt want someone comming into your homeland and taking away that income from you, right?