Answer:
Scorched Earth Policy
Step-by-step explanation:
Basically, Stalin ordered everyone to retreat and keep retreating, because Hitler had a biggo army. The Soviets just retreated and set fire to all buildings, because they said, "If we can't have it, you can't have it." (Not really, but it sounds cool.) The scorched earth policy made sure that Hitler get no resources if they continued, but they kept pushing anyways. The Germans had to leave Russia because it was way too cold, because it was winter, and the Russians were used to that.