I don't credit the victory over Nazi-Germany to any single country, but Soviet Union was the biggest player in the war against Germany. Germany's most losses came in eastern front.
No-one liberated Finland as we weren't conquered, hooray for that! But we did get help from Germany.
Communism stuff is another matter, as half of the Europe got under communism, but it is also worthwhile to mention that Europe was divided between allies, aka USA, UK, France, etc. made a deal with USSR to split Europe.
__________________
|