Answer:Well lad for one the soviets were suspicous because America was the only country to have an atomic bomb in their possesion. Second, the Soviets had started working on their own atomic bomb because of this discovery causing the Americans to become very on edge. Third, the Americans were already iffy with joining forces with the soviets because the soviets had already formerly joined the forces with the nazi regime or German wermacht. Lastly, at the end of WW2 Stalin began to get the ideas of communism and was kicked out of NATO because of that.
Hope this helps sum everything up and have a great day :)
Stay safe and stay awesome lad :)
and if you have any more WW2 related questions I'll be happy to help :D