Don't be fooling yourself that you have the strongest military in the world. Yeah your armed services are great, but your economy is not and a military without the money to run is not very powerful at all.
You forget, when World War II began, the U.S. was suffering through what we call the "Great Depression". Our economy was in ruins. It was the war that created the economic boom afterwards. We're not really even in a recession now, at least by the measures real economists use to define a recession.
Now, I'm not sure our population now is equal in perseverance, determination, or fortitude to the "Greatest Generation". At least not as a rule, in general. It would depend on who stepped up as leaders.