Secessionist spectators.

By the time Abraham Lincoln took office as president, seven southern states had seceded. Although Lincoln promised not to attack slavery where it existed, he did promise to halt its expansion. For southerners who viewed expansion necessary for the survival of slavery, this was unacceptable. The crisis came to a head at Fort Sumter, a U.S. post in Charleston Harbor. When Lincoln chose to reinforce the garrison in April 1861, Confederate forces demanded the fort’s surrender, and opened fire when their demand was refused. Residents of Charleston watched the bombardment of Fort Sumter from the city’s rooftops on April 12, 1861, knowing the attack meant war.

Source: Harper’s Weekly, May 4, 1861—American Social History Project.