Final answer:
The Battle of Fort Sumter began on April 12, 1861, when Confederate forces bombarded the Union garrison, forcing its surrender and marking the start of the Civil War.
Step-by-step explanation:
The Battle of Fort Sumter marked the commencement of the Civil War on April 12, 1861, when Confederate forces opened fire on the Union garrison stationed at the fort in Charleston Harbor. President Lincoln had announced his intention to resupply the fort, which had been cut off from needed provisions. The Confederates viewed the resupply as an act of aggression and subsequently bombarded the fort, resulting in its surrender after a 33-hour siege. This event influenced states like Virginia, Arkansas, Tennessee, and North Carolina to secede from the Union and join the Confederacy in the following months.