What battle made the union retreat back to Washington D.C.?

The First Battle of Bull Run, fought on July 21, 1861, marked the first major battle of the American Civil War and resulted in a Confederate victory. The Union forces, under General Irvin McDowell, were initially hopeful of a quick victory, but faced fierce resistance from Confederate troops led by Generals Thomas Jackson and P.G.T. Beauregard. The Union's defeat led to a chaotic retreat back to Washington, D.C., shattering the North's expectations for a swift end to the conflict. This battle underscored the war's potential for prolonged and bloody engagement.