But if a robber walks into a bank, speaks politely to all while pointing a gun & demanding the loot, and then escapes without hurting anyone -- it is still a bank robbery, still unlawful, still subject to criminal prosecution and penalties.
The fact is that secessionists seized dozens of major Federal properties, including forts, ships, arsenals and mints.
If you wish to argue that some of those were not actually Federal property, that they had always been state property, then in fact they were not "seized", merely re-occupied.
But that is not what history records.
History says those Federal properties were "seized" by force, some even before their states formally declared secession.
It makes those occupations illegal and provocations for war.
President Buchanan approved and sent the the sloop-of-war Brooklyn with 90 men from Ft. Monroe, Hampton Roads, to reinforce Ft. Pickens. The Brooklyn, had also been sent days earlier to help the Star of the West, loaded with war materiel and soldiers, in her attempt to aid Ft. Sumter, another aggressive move.
Then, on January 27 the Union Navy Department dispatched to Ft. Pickens at Pensacola, Fla., more reinforcements. It was the warship Brooklyn that sailed from Norfolk, Va., under sealed orders, taking the companies of men from Fortress Monroe. A newspaper freely reported she was destined for Ft. Pickens.
March 11 .....newly inaugurated President Lincoln directed
that Ft. Pickens be reinforced and the man-o-war Mohawk left New York harbor that day with orders to Capt. I. Vodges, 1st U.S. Artillery, directing him to transfer immediately his two companies from the ship Brooklyn to Ft. Pickens.
At the end of that week, The federal fleet off Ft. Pickens included the Sabine (50 guns), the Brooklyn (25 guns), the St. Louis (20 guns), the Crusader (eight guns), the Wyandotte (five guns) and the Supply (two guns).
President Abraham Lincoln issued a direct order to Capt H. A. Adams of the Man-o-war Brooklyn, lying off Pensacola, to land troops from his vessel at Ft. Pickens.
So if it is predisposition to aggression, you have it with two US presidents.