The First Battle of Bull Run, the earliest important engagement of the war, was fought on July 21, 1861, between a Union army of about 30,000 under the command of General Irvin McDowell and a Confederate army of about 22,000 commanded by General Pierre Gustave Toutant Beauregard.
Both sides were ill-trained for war, but a Union order to blockade the South and public pressure in the North led to a march, accompanied by many spectators, toward the Confederate capital at Richmond. At Bull Run the Union troops encountered the Confederate forces coming from their base at Manassas, about 4.8 km (about 3 mi) south of the stream. The 5-hour battle began with a Union assault resulting in a Confederate retreat to Henry House Hill. There, a part of a brigade commanded by General Thomas Jonathan Jackson held back the Union troops until 9000 reinforcements under General Joseph Eggleston Johnston arrived. The stubbornness of his defense earned for Jackson the nickname Stonewall.
Although the flight of the Union army did not end until the troops reached Washington, the Confederate forces were too disorganized to pursue. The Union army lost about 2900 men killed, wounded, captured, or missing; the Confederates, about 2000. The Confederate victory encouraged the South and spurred the North to greater effort. The battle, demonstrating as it did the effectiveness of the Confederate army, changed the status of the conflict from a rebellion to a civil war.