Moral equivocation on your part. The US is not a totalitarian regime threatening to nuke someone just for the hell of it! Come to think of it, if we were so inclined IT would have happened like in '46. Can you understand the difference now ?
Never said the US was a totalitarian state, but to be honoest, the US and England did use extensive terror bombing from 42-45 to specifically destroy the civilian population of Germany and Japan. As for 46, there was no capability to breach Soviet air defense and air force screens to deliver a decisive strike. Furthermore, such an action would have handed Stalin an excuse to take the rest of Europe, again, something no one wanted...one of the main reasons Patton was replaced, so that he wouldn't give an moral excuse for further war.
As for first strike, the US has always maintained a doctrine of first strike, willing to escalate to nuclear weapons use for a variety of reasons that do not include being hit first by nuclear weapons. Fact is, nuclear weapons become a deterent once the other guy has them, a political tool.