Um, didn't the south start it?
Um...no.
Lincoln’s dishonesty toward reinforcing Sumter was the start. Major Anderson was being provided food and sustenance by Beauregard. There were no casualties inflicted by the bombardment of Sumter. The casualties occurred when one of Major Anderson’s cannon blew up as they were firing an honorary salute to the Confederates after the fort was surrendered. Anderson’s men were tended to and fed well since the North didn’t take care of them. Lincoln manipulated and forced the South’s hand as they had turned over dozens of installations in the South without nary a peep. Sumter was in the South. Any historian can tell you the facts about Sumter.
“Um, didn’t the south start it?”
Actually, no. If you recall your history (but then, maybe you don’t), first Buchanan, and then Lincoln attempted to send reinforcements and supplies to Fort Sumter (after Fort Moultrie was evacualted because it was less defensible than Sumter). That, in itself was an act of aggression towards South Carolina, which had already seceded. South Carolina fired on Sumter to prevent the reinforcement and resupply of a hostile military reservation in its own harbor (i.e., Charleston Harbor).
Look at it this way:
Who would be the aggressor? North Vietnam for sending troops and supplies to a fort it occupied in South Vietnam, and refused to relinquish after North Vietnam and South Vietnam split; or South Vietnam for firing artillery to stop that reinforcement and resupply?
In that scenario I would argue that North Vietnam initiated the conflict, and thus was the initial aggressor.