What was Fort Sumter?
Fort Sumter, located at the entrance to Charleston Harbor, was the site of the beginning of the Civil War. When the Lower South states, including South Carolina, seceded from the Union, the problem of what to do with federal military installations in the new Confederate States of America became of paramount importance. Many of the forts were simply abandoned, but newly inaugurated president Abraham Lincoln drew a line at Fort Sumter, and instructed the garrison there, commanded by Major Robert Anderson, not to evacuate.
Secessionists realized that they could not be taken seriously if the fort in the middle of Charleston Harbor was allowed to remain in federal hands, and they surrounded the harbor with batteries of artillery. Lincoln, realizing that reinforcing the fort with troops would be interpreted as an act of war, decided instead to send supplies. The crisis came to a head at 4:30 am on April 12, 1861. The batteries opened fire on the fort, which surrendered after a 34-hour bombardment.
President Lincoln responded to the attack by calling for 75,000 volunteers to put down the rebellion, and this act resulted in the states in the Upper South (Virginia, Arkansas, Tennessee, and North Carolina) leaving the Union to cast their lots with the Confederacy. It also inaugurated the war, which after an almost bloodless beginning (the only Federal casualty was killed by an explosion after the battle was over) but would go on to become the most costly in American history.