The battle of stalingrad.
but Stalingrad erased the largest single Army in the German arsenal from its inventory, obliterating scores of divisions and their men. It was the first time a Field Marshal went in the bag. It was the end of the Germans controlling the initiative and offensives in the East. After that, they were limited to counterattacks -- big ones, like Manstein's and Kursk, but counterattacks all the same. It had a huge impact on German morale, bringing the first cracks in the Nazi facade. After Stalingrad (and very much too late), Goebbels called for "Total War" in a Germany that was still producing Bechstein pianos. Stalingrad was part of a crescendo of Axis defeats during a 90-day period that turned the war around: Guadalcanal, New Guinea, Alamein, and the Barents Sea. I would have to say that the big point in Stalingrad was that before that battle, Nazi propaganda was about Germany's "New Order" for Europe and the world. After Stalingrad, the tone shifted. Suddenly Germany was now the defender of Western civilization against Bolshevism. Even Goebbels recognized that Germany as on the defensive after Stalingrad.