I wouldn't say USSR was the only one concerned, both sides were suspicious about each other. The Russian thought they will be betrayed during the war, its very hard to explain but i will put it in short. USSR is communist and therefore america did not like communism and so the russians didnt trust the Americans. both sides wanted to spread there influence of ideology
Explanation:
both sides already didnt like each other since ww1 but had to throw away the hate for now to beat germany.
