The First Battle of Bull Run, also known as the Battle of First Manassas, was the first major battle of the American Civil War. The battle was fought on July 21, 1861, in Prince William County, Virginia, just north of the city of Manassas and about 30 miles west-southwest of Washington, D.C. The Union's forces were slow in positioning themselves, allowing Confederate reinforcements time to arrive by rail. Each side had about 18,000 poorly trained and poorly led troops in their first battle. It was a Confederate victory, followed by a disorganized retreat of the Union forces.
Just months after the start of the war at Fort Sumter, the Northern public clamored for a march against the Confederate capital of Richmond, Virginia, which was expected to bring an early end to the Confederacy. Yielding to political pressure, Brig. Gen. Irvin McDowell led his unseasoned Union Army across Bull Run against the equally inexperienced Confederate Army of Brig. Gen. P. G. T. Beauregard camped near Manassas Junction.