The event that marked the beginning of the Civil War in the United States was the attack on Fort Sumter on April 12, 1861. As tensions between the Northern states and Southern secessionists escalated, the Confederate forces fired upon the fort, which was a federal stronghold in South Carolina. This assault prompted President Abraham Lincoln to call for troops to suppress the rebellion, officially igniting the conflict. The Battle of Fort Sumter symbolizes the start of a brutal war over issues such as slavery and states' rights, profoundly impacting the nation's history.