The First Battle of Bull Run, fought on July 21, 1861, in Virginia, was the first major battle of the American Civil War. Union forces, under Brigadier General Irvin McDowell, attempted to advance on Confederate troops led by General Pierre G.T. Beauregard and General Joseph E. Johnston. Despite initial Union success, Confederate reinforcements turned the tide, causing the Union troops to retreat in disarray. The Confederate victory shattered illusions of a quick war, setting the stage for a prolonged conflict.