We can argue that the Cold War was caused by fear because it was each side’s fear of the other that led it to take the steps that led to the Cold War. The Cold War, in this view, did not arise because of what either side actually did. Instead, it arose because of what each side was afraid the other might do.
For example, we can clearly say that Stalin’s actions that led to the Cold War came about because he was afraid of the West. Stalin knew that Russia had been invaded from the west a number of times in its history. He was afraid this might happen again. Therefore, he insisted on Soviet control of Eastern Europe to serve as a buffer against invasion.
Similarly, we can say that American actions were motivated by fear. The US was afraid that communism was an expansionistic ideology that would try to take over the whole world. Thus, when Stalin took control of Eastern Europe, the US interpreted that as a frightening step towards world domination.
Thus we can say that both sides were acting out of fear of the other. They were not reacting to actual aggression but to their own fear of aggression.