In a must-win clash, Union forces halted the northern invasion of Robert E. Lee\\'s Confederate Army. The Union\\'s eventual victory in the Battle of GettysburgBattle of GettysburgOne of the largest military conflicts in North American history begins on July 1, 1863, when Union and Confederate forces collide at Gettysburg, Pennsylvania. The epic battle lasted three days and resulted in a retreat to Virginia by Robert E. Lee\\'s Army of Northern Virginia.