At 4:30 a.m. on April 12, 1861, months after seven Southern states had seceded from the Union, a single mortar was fired by Confederate soldiers at Fort Sumter near Charleston, South Carolina. After a brief battle, during which no one from either side was killed, Major Robert Anderson surrendered on April 13 and evacuated the fort, carrying the flag with him. Responding to the rebellion, President Abraham Lincoln called for 75,000 volunteer troops to be mustered in the next 90 days, and the American Civil War was under way. In this photograph, taken by Samuel A. Cooley, Union troops aimed mortars at Fort Sumter in an effort to reclaim it in September 1863. On April 14, 1865, Anderson returned to the fort and raised the flag once more.