The south seceded for both reasons. Prior to the Civil War, the South lived in the antebellum period which was a period of great economic success built around their agriculture and cotton plantations which was largely accredited to their slaves who provided free labor. The south believed that states rights protected their way of life and successful economy and they also believed the northern states were infringing on these rights and would take away the source that built such a great and successful economy. Because the slaves built their empire and they believed states rights protected this, they succeeded to keep their way of life.
The South seceded over states' rights. Confederate states did claim the right to secede, but no state claimed to be seceding for that right. In fact, Confederates opposed states' rights that is, the right of Northern states not to support slavery.
