The German invasion of the Soviet Union,
Russia fights back,
Inspired by economic, ideological and strategic, Hitler ordered the invasion of Russia. On 22 june 1941 Operation Barbarossa took the Soviets by surprise. By blitzkrieg tactics, the three million Germans strong force struck deep into Russia, capturing whole Russian armies. By winter the German advance stopped on the outskirts of Leningrad and Moscow. The harshness of the climate, the resilience of Russia had taken their toll, the Germans were very tired.
Russia fights back. In december 1941 the Soviet Union surprised the Germans by a counter-offensive, slow down the threat on Moscow. Germans attention went to the south and attacked in the Caucasus in the spring of 1942. Hitler's army suffered massive defeats at Stalingrad and at the battle of Kursk in the summer.
The great losses of the German army were in stark contrast to the apparently limitless Soviet resources of men and material. The Germans were driven back from Soviet territory.