Secession wasn't the official start of the war, I would say it was Sumter, which happened shortly after Lincoln took office. I was going to mention Lincoln, bu

Secession wasn't the official start of the war, I would say it was Sumter, which happened shortly after Lincoln took office. I was going to mention Lincoln, but he was in office during Sumter and when he died, Lee had already surrendered the confederate army. It's fairly fuzzy too because there were battles after the surrender.