First of all, the Confederacy had no legitimate claim to Fort Sumter -- zero, zip, nada -- since it was a Federal fort, built on Federal property, with Federal funds and manned by Federal troops.
So any threats against those Federal troops were necessarily acts of rebellion and/or war.
But second, and more to the point: Confederates' assault on US forces, and seizure of Fort Sumter, were absolute acts of war against the United States, regardless of how "justified" Confederates may have felt themselves.
That Confederate assault was equivalent to the Japanese December 7, 1941 attack on Pearl Harbor.
It created a state of war.
Third, it was also an existential assault on the United States itself, since the immediate result was to convert four Union states with double the population of the original seven and those four had already voted against secession.
Fort Sumter caused them to change their votes to secede -- Virginia, North Carolina, Tennessee and Arkansas.
Finally, their success in military action at Fort Sumter lead the Confederacy to attempt similar military success in three more Union states which refused to secede -- Maryland, Kentucky and Missouri.
Those three states would again double the population of the Confederacy's original seven, if they joined it.
Loss of those last three states would, in the opinions of Union leaders, lead to destruction of the United States.
Bottom line: any claim that the Confederacy "just wanted to be left alone" is ludicrous, since from Day One it assaulted and seized every United States property and territory it could reach.
You da’ man!
:)
The pretended confederacy just wanted their own states, and all the states next to them.