After world war 2, why did the Soviet Union consider the United States a threat?

The United stars was the first country to develop an atomic weapon. The soviet was sure that they were going to betray them and bomb them with their atomic weapon, considering they were on the same team. The soviet sent a spy to make sure if their hypothesis. The spy reported back saying they were planning to bomb them. The soviet decided to bring war first.

Considering we had nuclear weapons now and they didn't

That was probably it