This article by the Daily Beast addresses the main issue driving Southern Succession and leading up to the Civil War. Amazing that we are still debating this:

The Ordinance of Secession and “Declaration of the Immediate Causes” drafted by South Carolina grandees intent not only on justifying their own state’s withdrawal from the Union in December 1860, but on persuading the other slave-holding states to join it, was concerned entirely and exclusively with the question of slavery. It quoted the Constitution. It cited the Declaration of Independence. But it was not about all men being created equal. And it was not about tariffs, as some have argued since. And it was not merely about the general principle of states’ rights. It was specifically about the states’ rights to enshrine slavery, pure and simple—and evil—as that was, and the obligation of the federal government to guarantee the rights of human-property owners. Since the Feds weren’t likely to do that under the new Lincoln administration in Washington, the Carolinians argued, “self-preservation” dictated secession. They were determined, come what may, to make their world safe for slavocracy.

More on the role of slavery in the Civil War here.