I would say one of the critical contributors to the Cold War was the ideological conflict between the Soviet Union and the United States. Ultimately, it pit Free Enterprise and Western Democracy against Single Party Communism, two very different, and mutually opposing, world views. The two mindsets did tend to perceive in the other an existential threat—capitalistic countries and communist countries tend to be mutually antagonistic, and this did not actually originate in the Cold War. We can look all the way back to the writings of Marx, with his prophesy of global revolution, or at the calls for international revolution by Trotsky, or (in the US) we can consider the Palmer Raids, to give a few examples on this theme, each example preceding the Cold War itself.
However, to really understand the beginnings of the Cold War, you need to look at the political realities which emerged after World War II. Ultimately, the picture which emerges is this: in the close of the war, Nazi Germany was being pushed back from two different sides: the Soviets sweeping through Eastern Europe and the Allies coming from the West. After the end of the war, the Soviet occupied territories remained under Soviet control. This resulted in the descent of the Iron Curtain, with the Soviets creating in Eastern Europe a series of buffer states under the political domination of the Soviet Union. It was in this context that large scale bipolarization under the Cold War took shape.