I hate to get involved in this thread but if you're talking about Fort Sumter, the facts are clear. They were Asked Politely to leave after being told that South Carolina was no longer part of the Union.
They could have walked away, but they stayed as unwanted interlopers. The rest is history.
So if I ask you politely to give me your house would you do it?
The fort belonged to the United States of America. It wasn’t their place to be evicting US troops from a US fort - politely or otherwise.