[BluffTHIS!]

Although I've made clear in this thread that I think the North was morally justified in fighting the war solely to free the slaves, and gave a little of the history re Ft. Sumter, the South's argument would go like this:

1) Upon secession, in which South Carolina ceased to be part of the federal union, there could exist no federal property within the boundaries of South Carolina.

2) In consideration of the above, the refusal of Federal troops to vacate installations in South Carolina constituted tresspass and forcible occupation.

3) South Carolina and its southern allies were then justified in using force to remove federal troops and recover property now belonging to South Carolina, the same as if a 3rd country had invaded the US.