This article http://www.johndclare.net/Basics_ColdWar.htm breaks down the main reasons for why USA and USSR became rivals; thus it highlights that USA and the USSR became rivals due to different ideology. Moreover, the article reveals that Stalin had found it hard to forgive USA and Britain for supporting the whites against the Bolsheviks in the Civil Wars (1918-1921), and he believed that they had delayed D-Day in the hope that the Nazis would destroy Russia. Furthermore, the article goes on to mention the main disagreements at Yalta and Potsdam; for instants at Yalta there was a disagreement about what kind of government was to be set-up in Poland, as well as, how much money USSR was to receive from Germany.
Additionally, at Potsdam the article mentions how Roosevelt was replaced by a much anti-communist president, named Truman. When Truman came to power he believed that both USA and Britain where too soft on Stalin at Yalta, so he had felt it was his job to be tough on Stalin. And he showed that by the dropping of the atomic bomb. (This article also includes the Truman doctrine, the Marshall Plan, the Berlin blockade, the Korean War and finally Poland and Hungary)
This article http://www.gcsehistory.org.uk/modernworld/coldwar.htm focuses on the key events and how they created tension between USA and USSR, as well as how it developed the cold war. For instants the article highlights how West Germany had been allowed to join NATO, thus creating tension between USSR and USA, as it bought back the memory of World War Two and how Germany had caused so much damage to the USSR. http://2001-2009.state.gov/r/pa/ho/pubs/fs/85895.htm