I never see another reason listed as why the bombs were dropped. We had developed a bomb that was a city killer. We also knew that the Soviets were our next enemy. So what to do? Most of the world would not believe there was one bomb, one killed city. So to remove doubt and prove American superiority drop the bomb, kill a city, show the world America is the most powerful country in the world by a large amount.
Unfortunately at that time, traitors were already giving the Soviets information about the bomb.