Question

How did the involvement of the U.S.S.R. in WWII help it to spread communism in eastern Europe?

Answer 1

The Red Army occupied Estern Europe countries after beating the Nazis. So Stalin considered it was his right to set the kind of regime he wanted to (communism of course). Then Soviet soldiers stayed for a long time after 1945 in these countries too. And the Soviet Army also "helped" (of course by using coercition) these countries to refuse the Marshall Plan. Remember Katyn too, where the Soviets killed thausend of polish officers, in order to eliminate the threat of a future rebellion.