There are at least three ways of looking at this.
First, we can look at the ultimate causes of the Cold War. The ultimate cause of this conflict was the fact that the Soviet Union was communist while the United States was a capitalist and democratic society. These two ideologies were very much opposed to one another. This meant that the two countries would have a very hard time trusting one another.
Second, we can look at an intermediate cause of the Cold War. This was the fact that World War II created a world in which the US and the USSR were the two main powers. WWII forced the US to become a major military power. It also badly damaged other countries like France, Germany, and the UK which might have had aspirations to superpower status. Therefore, the war ended with two superpowers that were suspicious of one another.
Finally, we can say that the events of the ending of WWII were the immediate cause of the Cold War. Specifically, the Cold War was caused by the Western reaction to the Soviets’ demand for more control over Eastern Europe. When the Soviets took power over all of Eastern Europe, and when communists showed signs of interest in moving into Turkey and Greece, the West was very worried. The West felt that this was the communists’ first move towards world domination. Their desire to prevent this led to the Cold War.