At the start of the cold war, what factor created a risk of war between the allies and the soviet union

At the beginning of cold war, the communist influence on the democratic countries of Eastern Europe created a risk of war between the allies and the Soviet Union.

Soviet Union freed the Eastern Europe countries from the grasp of the German Nazis. During cold war, the countries such as India, Yugoslavia, and Indonesia helped in achieving the neutrality. This war didn't use the armed combat much but both the sides had nuclear strategy which would have led to nuclear world war.

But after the war was over, the allies (the United States and Great Britain) started fearing that the Soviet Union would be successful in establishing their permanent communist dominance over the democratic Eastern Europe countries. This ultimately created a risk of another war.

when the united states took over