The Confederate bombardment of Fort Sumter (April 12–13, 1861) shocked the North. Newspapers framed it as an assault on the flag and the Union itself. Public sentiment shifted rapidly from compromise to uncompromising resolve.
Lincoln's call for 75,000 volunteers was met with overwhelming response—state quotas filled in days. Men enlisted from farms, factories, and cities; women organized aid societies. Even previously anti-war Democrats (e.g., Stephen Douglas) rallied to the Union cause.
"War Hawks" in the Republican Party gained momentum. The attack unified disparate factions—abolitionists, Free Soilers, Unionists—into a cohesive war effort. The Confederacy's gamble backfired: it transformed a sectional crisis into a national crusade to preserve the United States.