also no one has brought up the fact that the US was in many ways built on WWII. Without it the US would never have been what it is today. And if we were to end WWII before it begain, if it were even possible, the ramificatiosn would be unimaginable. Britain would not be our close allie, on the contrary they might actually despise us. There was a lot of nazi sympathy in britain pre-WWII. The cold war might have never happened, we could have instead went into all out war with russia, seeing as we would be occupying germany, a MAJOR player in diplomacy in europe. If you thikn we have alienated ourselves from the rest of the world now... imagine if it wasnt muslim extremest that lack modern militaries. Imagine instead that it was a 'coallition' of european super powers. Britain, France, Russia, Italy, ect ect. We would have been like napolean, but way worse. Atleast he was from europe, atleast he belonged on taht continent. Trust me, america would not have it easy.
And let us not forget the Japanese. They didnt just get phoned by Germany one day, and decided it would be a good idea to go take over the pacific. That was brewing for just as long if not longer them what was going on in Europe. We almost surely would have been involved in the Pacific war still, and without allies backing us in europe, shit woulda got real hectic real fast.