In early April 1861, Confederate authorities pressed the small U.S. garrison at Fort Sumter (in Charleston Harbor) to leave. The standoff mattered because the fort became a test of whether the federal government would keep its military presence in the seceded states.
Before dawn on April 12, Confederate batteries opened fire on Fort Sumter. The attack marked the start of open warfare between the United States and the Confederacy, turning a political crisis into an armed conflict.
After about 34 hours of bombardment and worsening conditions inside the fort, Major Robert Anderson accepted surrender terms. The surrender helped trigger rapid mobilization on both sides and persuaded many Americans that compromise was unlikely.
On April 15, President Abraham Lincoln issued a proclamation requesting 75,000 militia to suppress what the administration described as an insurrection. This call for troops escalated the crisis, pushing some Upper South states toward secession.
On April 17, Virginia’s secession convention voted to dissolve the state’s bond with the United States. Virginia’s decision was a major turning point because it moved the center of conflict closer to Washington, D.C., and made Richmond a likely Confederate capital.
On April 19, Lincoln proclaimed a blockade against Confederate-controlled ports, aiming to restrict trade and war supplies. The blockade became a cornerstone of the Union’s long-term strategy and helped shape how foreign governments viewed the conflict at sea.
On April 19, violence broke out in Baltimore as Union troops passed through the city, leaving soldiers and civilians dead and wounded. The unrest highlighted how fragile Union control was in the border states and complicated the defense of Washington, D.C.
On April 27, Lincoln expanded the blockade to cover additional seceded states’ coastlines, including Virginia and North Carolina. This extension signaled that the conflict was widening and that the Union planned sustained naval pressure rather than a brief show of force.
Early in the war, General-in-Chief Winfield Scott proposed a strategy later nicknamed the Anaconda Plan: blockade the South and gain control of the Mississippi River to split the Confederacy. While debated at the time, its focus on economic and geographic pressure influenced Union planning beyond the first battles.
On June 3, Union forces attacked Confederate troops at Philippi (in what is now West Virginia) and drove them off. Though small, the fight showed how quickly the war spread beyond Charleston and foreshadowed a separate Unionist political path in western Virginia.
On July 16, Union general Irvin McDowell led his largely inexperienced army out of Washington to strike Confederate forces near the railroad junction at Manassas. The movement opened the first major campaign in northern Virginia, with the Union hoping a quick victory could end the rebellion.
On July 18, Union troops clashed with Confederates at Blackburn’s Ford along Bull Run. The fighting convinced McDowell that a direct assault was risky, pushing him toward a flanking plan—and buying time for Confederate reinforcements to move.
In mid-July, Confederate general Joseph E. Johnston shifted troops from the Shenandoah Valley to Manassas Junction using the Manassas Gap Railroad. This rapid reinforcement was significant because it helped concentrate Confederate forces in time for the coming battle and demonstrated the growing military importance of railroads.
On July 21, the Union and Confederate armies fought the First Battle of Bull Run (First Manassas) near Manassas, Virginia—the first major battle of the Civil War. Confederate forces held and counterattacked, sending the Union army back toward Washington and making clear the war would not be short.
In late July, Congress passed the Crittenden–Johnson Resolution, stating the war’s purpose was to preserve the Union rather than to interfere with slavery in the states. The measure reflected the political need to keep border-state support and showed that Union war aims were still contested in 1861.
The defeat at Bull Run forced the Union to reorganize and plan for larger, longer campaigns instead of a quick march on Richmond. By late July 1861, the opening phase that began at Fort Sumter had ended with both governments mobilizing for a prolonged conflict across multiple fronts.
Fort Sumter and the Opening Campaigns (April–July 1861)