Why did the US and Russia become enemies after World War 2?

The US was distrustful of the USSR and their leader Josef Stalin after the war because he refused to allow certain agreementsto be carried out. While there is considerable disagreement over who is At Fault, even to this day, their is no question that President Franklin D. Roosevelt felt he had a different understanding of what the USSR would live up to than did the USSR at the end of the war in Europe, in April, 1945. For example, the US had thought Poland was to have free elections, but the USSR refused to allow this. As a result of this and many other disagreements involving many of the eastern Euroopean countries (Bulgaria, Yugoslavia, Germany...which was split into East and West Germany, Czechoslovakia and others)...the US and USSR entered into what became known as the Cold War. Meaning it was a war of Words and not weapons...so cold not hot.