 The two sides would suffer over 45,000 casualties, the largest number of any single engagement of the war. Almost a third of all Confederate officers were killed, wounded, or captured. And in the end, Union forces would hold the Confederates off and win the battle, causing Lee to retreat his army back to Virginia. This victory, coupled with the Union victory at Vicksburg, Mississippi on July 4th, would spell the beginning of the end for the Confederacy.