States had the right to secede. The War Between the States was not launched to free slaves. Lincoln believed that whites were superior and favored the deportation of freed slaves. The South was for free trade; the North wanted protectionism.
The compact theory states that separate sovereign states compact together without losing any of their sovereignties. The United States are. The Constitution was ratified by the sovereign peoples of each state individually. Secession is natural and understandable with this theory, as is nullification. States rights is the model against empire.
The phrase the United States is reflects the nationalist theory. Neither secession nor nullification is legitimate under this way of thinking. There were no thirteen states. They were just a single people. When does this happen when thirteen separate independent states become a single people? This theory created the modern state from federated polities. The original decentralized system became a single state – an empire. It was a crime against humanity.
Lecture 5 of 14 from Tom Woods' The Politically Incorrect Guide to American History lecture series.