A story could be written about the US having the bomb in early '4' and dropping it on Moscow. Japan and Germany would surely have surrendered at that example, and the obvious future enemy would have been 'neutralized'. America would have been standing astride the world it the biggest army, the biggest air force, the biggest navy and the 'baddest' weapon.
Well a couple issues I have with that is- why would the United States have dropped an atomic bomb on its most powerful ally in 1944? The U.S. had spent the better part of 3 years telling the American public that the brave Russians were our allies- and then we dropped the most powerful weapon we had on Moscow?
And secondly- why do you think that the Soviets would have surrendered if we dropped an atomic bomb on Moscow? The bulk of their military forces were in Western Europe then, and the bulk of their industrial might was east of the Urals by then.