The First Battle of Bull Run took place on July 21st 1861 and was the bloodiest one up to that moment. This battle “shattered the Union’s hope of winning the war quickly and easily” since it was demonstrated that both sides (Union and Confederates) were poorly trained and inexperienced and they had to prepare themselves for a long and bloody war.
This first battle was won by the Confederates and the Union soldiers had to retreat from it.