Gettysburg

The battle of Gettysburg was often described as the turning point of the war due to heavy casualities.  Both sides of the battle suffered a massive 23,00 casualities, which is 46,00 total casualities.  Although both lost the same amount of soldiers, it was a victory for the North, because they had more soldiers to spare, and it stopped general Lee's invasion of the North.

Image: http://www.prx.org/pieces/98152-gettysburg