As Jefferson Davis said on the Senate Floor, January 10, 1861:
...the tenth amendment of the Constitution declared that all which had not been delegated was reserved to the States or to the people. Now, I ask where among the delegated grants to the Federal Government do you find any power to coerce a state; where among the provisions of the Constitution do you find any prohibition on the part of a State to withdraw; and if you find neither one nor the other, must not this power be in that great depository, the reserved rights of the States? How was it ever taken out of that source of all power to the Federal Government? It was not delegated to the Federal Government; it was not prohibited to the States; it necessarily remains, then, among the reserved powers of the States.
I've read a fair amount of Davis's speeches and writings and seen nothing that indicated that Davis ever had more than a passing knowledge of the Constitution. The 10th Amendment talks of powers delegated to the United States AND powers prohibited to the states. Powers to approve changes in status were powers delegated to the United States. Actions that had a negative impact on the other states were actions denied to the states. Implied in both of these is unilateral secession.