Following Beauregard's bombardment in 1861, Confederate forces occupied Fort Sumter and used it to marshal a defense of Charleston Harbor. Once it was completed and better armed, Fort Sumter allowed the Confederates to create a valuable hole in the Union blockade of the Atlantic seaboard.
This led to the secession of some of the southern states. When President Lincoln announced he was sending unarmed ships to resupply Fort Sumter, the South had to decide if they would stop these ships or allow them to go to Fort Sumter. The South decided to attack the ships, leading to the start of the Civil War.
