The event marking the beginning of the U.S. Civil War was the attack on Fort Sumter, located in Charleston Harbor, South Carolina, on April 12, 1861. Following the secession of several Southern states from the Union, tensions escalated as Confederate forces opened fire on the fort, where Union troops were stationed. This bombardment lasted for 34 hours, resulting in the fort's surrender. The attack galvanized support for the war among Northerners and shifted public sentiment in favor of a military response to preserve the Union. The conflict that followed would become one of the bloodiest in American history, fundamentally reshaping the nation.