Which event officially started the civil war

The attack on Fort Sumter. I hope this helps.

On April 12, 1861, Confederate warships turned back the supply group to Fort Sumter and opened a 34-hour attack of bombs continuously  on the stronghold. The garrison surrendered on April 14. The Civil War was now beginning . On April 15, Lincoln called for 75,000 volunteers to join the Northern army. hope this helps I got this from my history text book