Seizure of federal property is an act of war. Arsenals all over the South were raided for arms, another act of war.
The Idiot Cabal managed to maneuver Lincoln (against his desire) into having to protect federal property and Sumter was federal property deeded to the feds by the State of South Carolina. Thus, he had no choice but to use military means.
And pray tell, what good were British deeds after the Colonies declared independence?
King George III owned all the colonies. Were we supposed to respect his claims to the land because he had papers that said it was his?