How many Nazis and Japanese emporer-worshippers, all well-armed, were there?
We didn't just beat the Germans and the Japanese militarily; we converted them to our way of thinking. We got them to see that living in a Constitutional republic is a lot better than kowtowing to the emperor or the Fuhrer. That's what needs to happen here. Look at the quagmires we got ourselves into in Vietnam, Afghanistan, and Iraq. That is what happens when you win the war but not hearts and minds.
There’s a world of difference between WW2, on the one hand, and Vietnam, Afghanistan and Iraq, on the other. It was how we conducted ourselves. WW2 was viewed (correctly, IMHO) as a literal war for survival. We held back NOTHING, and we went into that war knowing that we were either going to destroy those governments or they would destroy us - there was no other option. As Ike called it in his memoirs, it was a Crusade (in Europe) - and it HAD to be, otherwise we couldn’t have won, because there’s no other way that you get 1 in 10 people in the country into uniform for an indefinite period of time. So, because of that 100% effort, we won - and occupied both nations (and let’s not forget that the Russians took and inflicted several times more casualties from/to the Germans - but I’m discussing our behavior). The reason why they changed to Constitutional republics is not because they loved us - it is because we utterly smashed their prior governments and literally gave them no choice. Only after a few years of operating like that, and getting lots of our aid, and lots of our trade, and seeing the prosperity that they were enjoying - and the security because WE provided it - ONLY THEN did they make the emotional decision that living in a democracy was far better than what they had 10, 15, 20 years earlier.
In our last three wars, it was NOT a fight for our survival. We held back militarily because of domestic political reasons. Yes, we militarily controlled territory within each country, but we made it plain that we weren’t going to do to them what we did to Germany and Japan. Once the other side understood that, they knew that they just had to hang on for a while in order to survive and keep their way of life going. So that determination, combined with a lot of Russian and Chinese (and Iranian, in the case of Iraq) military aid and propaganda support, led to us getting tired of these wars that weren’t, after all, in our vital interest in anything like the way that WW2 was.
Those things, IMHO, account for the vastly different results in those wars.