What caused the tension between the soviet union and the us

Stalin resented the Western Allie's delay in attacking the Germans in Europe and that the United States had tried to keep its development of the atomic bomb a secret.

Explanation:

Stalin always pressed England and the US to open another front during the 1940s as German forces were concentrating to deepen in the Soviet territory.

He believed the Western allies were on purpose to profit from the weakening of the USSR as it fought against Nazi Germany.

The delayed had enabled Nazis to redirect manpower to the Eastern front.

Stalin was annoyed since he believed the US and Britain delayed to open the second front against German troops in the West, and demanded a buffer formed from Baltic nations and Poland after the war.

The development of the atomic bomb was jealously held by the US, as it gave the supremacy on the overall outcome of the war and its unrevealing by alleged "spies" meant that the USSR and the US would start an arms race.

The rivalry in atomic weapons was quickly contested in the 1950s and soon to be followed by the space race.