From: The Battle of Russia - Wikipedia, the free encyclopedia
"In order to justify the Western Allies alliance with the Soviet Union, the episode, like the entire Why We Fight series, misportrayed or simply omitted many facts, which could have cast doubts on the "good guy" status of the Soviets, such as the Nazi-Soviet alliance, Soviet invasion of Poland; Soviet occupation of the Baltic States, Winter War and others.[1] Virtually in line with the Soviet propaganda, the series was not only screened but widely acclaimed in the Soviet Union.[2] To exonerate the Soviets, the series casts even cast less important Allies, like the Poles, in the bad light.[1][2] The episode has been described as "a blatant pro-Soviet propaganda posing as factual analysis."
I think the "keeping" Eastern Europe might have been a factor. Maybe the Berlin Airlift/ Wall too.