The South knew they would be attacked, despite what the Northern politicians told them, and they didn’t want an outpost on their territory.
It would have been an interesting dilemma, if Jefferson Davis had been able to order South Carolina not to fire on Fort Sumter. Otherwise, the Federal property had been relinquished without violence. He could have then said, ‘How about us Tennesseans sit down and talk?” Such an event would not have been popular with the Manifest Destiny crowd.