Southerners justified secession with the theory of what?

Southerners justified secession with the theory of states' rights, arguing that individual states had the sovereign authority to determine their own governance and laws, including the right to withdraw from the Union. They believed that the federal government was overstepping its bounds, particularly regarding issues like slavery and economic policies. This perspective was rooted in the interpretation of the Constitution, which they argued allowed for such actions. Ultimately, this theory was a key ideological underpinning of the Confederacy during the Civil War.