The Soviet Union began their counterattack against Germany during 1942. Before this, the Nazi-Soviet Pact of 1939 made it so that the Germans would not enter Soviet territory. Once this pact was broken by Hitler in 1941, the Soviets began to prepare their counterattack. This counterattack officially begins in 1942 with the Battle of Stalingard. This became a huge turning point in World War II, as the Soviet Union gained momentum.
