One of the first causes of the Cold War is the fact that World War 2 had ended. During WW11, the United States and the Soviet Union had to work together and agree somewhat on ideas and plans. After the war ended, there wasn't a need to get along or agree.
The Marshall Plan was another big cause and factor of the Cold War. The Soviets didn't like the idea of the United States interfering with the countries around them to stop the spread of communism.
The Nuclear Arms race kept both countries on edge. Neither of them wanted to fall behind in case there was a nuclear war.
The Cuban Missile Crisis was another factor of the cold war because the americans were afraid of an nuclear war.
The Korean War was yet another conflict that added fuel to the Cold War. The United States and the Soviet Union got involved on different side of the war. They each fought for the side that had the same governing deals and standards as them.