Most of our immediate problems with Russia after WWII centered around Poland. Russia had liberated Poland from the Germans and when the war ended we assumed that Poland would be free for democratic elections. However, Russia had been invaded twice in the century and both times the Germans had come through Poland. Stalin was not about to let it happen a third time and so retained control over the nation. Truman threatened to cut off all economic aid to the Russians, which they desperately needed, if they did not release Poland. Russia felt protection was more important than aid so kept Poland and the relationship began to fracture between Russia and the U.S. that led to the Cold War.
Historically Speaking 