Battle of Gettysburg
Lee brought an army into Pennsylvania that numbered 75,054 men and lost 22,638 casualties or about 30% of his army. Meade lost so many field grade officers that the Army of the Potomac would not recover for the rest of the war. Both the Union I Corps and III Corps lost so many men they had to be combined with II Corps. The battle took more American lives than any other battle in United States history. Gettysburg is still the largest battle to ever be fought on American soil. The Union victory over the Confederacy ended Lee's invasion of the north. Lee would never try to invade the Union again. The Army of Northern Virginia would never get their strength back. However the supplies taken during their time in Pennsylvania would keep the Confederate army going. The wagon train of supply wagons and ambulances for the wounded was over  long. Lee never had more than 51,000 men the rest of the war. Numbers from the Union forces wore down Lee and his army. This is why Gettysburg is said to be the turning point of the American Civil War. After the battle the confederates figured out that there was a slave spy.