The significance of the Battle of Bull Run, fought in July 1861 during the American Civil War, was that it marked the first major battle and shattered the North's hopes of a swift victory. Union forces expected an easy win, but the Confederate army proved resilient, leading to a retreat by Union troops. The battle demonstrated the necessity of preparation and serious commitment from both sides in the conflict. Furthermore, it boosted Southern morale and underscored the war's potential duration, shaping subsequent military and political strategies.