Lincoln started the war at Sumter.
The first act of war was Anderson moving to Sumter from Moultrie, against the agreement made, while negotiations of the forts was taking place.
Then the next act of war, was the refusal to send Anderson back to Moultrie, when S. Carolina gave them the opportunity to avoid war.
Then the next act of war was to send the Star of the West to reinforce Sumter with troops, arms, and supplies.
Then later Lincoln took command and sent other ships to reinforce Sumter,
As far as the first 'shooting' act of the war, one could always point to John Browns invasion of Virginia.
Not stupid on the part of the South. You can't let the enemy remain in your country and reinforce it at will. Best to take care of him now while you can.
Quantrill