We did not respond proportionately, we responded disproportionately. I don’t know how this is even being argued by people that our response on WW2 to any of our belligerents was in measured proportion.
Like, it was the last time we went to total warfare and indiscriminately bombed civilian population centers
And certainly neither Germany nor Japan had any compunction about indiscriminately bombing civilians, let alone intentionally murdering many millions of them.
Walk softly and carry a big stick, is still applicable game theory and the big stick was not meant to be held back just because someone hit you with a smaller stick.
If you only respond in proportion to an adversary, they basically get to dictate the engagement. A strategy that leads to less violence overall is to apply disproportionate retaliation to any attacks, which signals to other players that you will make actions against you not a viable long term strategy
The Japanese tried to firebomb the US, too; they simply weren't as successful[0]. They also had a nuclear program, and God knows they would have nuked the US first if they could have. There was no Mutually Assured Destruction back then, either--just unidrectional Assured Destruction. I'm glad the US got there first.
Consider the handy Wikipedia chart of WWII deaths[1]. The main instigators of the deadliest war in history, Germany and Japan, have fairly low total death rates and, in fact, comparatively low civilian death rates compared to the Allies.
Further I want to point out that 'proportionate' is not the same as 'equivalent'. A proportionate response doesn't mean you try to kill exactly the same number of troops or sink the same number of warships.
Finally I want to reiterate that I do generally agree with you about the value and deterrent effect of some perceived probability of a disproportionate response, or at least the value of unpredictability in general. That is not to say that I believe the Madman Theory is an optimal strategy over the long term, but I do think it can be played effectively as a short-term tactic.
[0]: https://en.wikipedia.org/wiki/Fu-Go_balloon_bomb
[1]: https://upload.wikimedia.org/wikipedia/commons/thumb/d/d1/Wo...
Not only did the Japs attack Pearl Harbor, formally declare war on the United States, enjoy an alliance with Germany and Italy who themselves declared war on the Unites States, and conquer or attempt to conquer all those places to build their empire; they also fought fanatically and with exceptional brutality, they committed countless atrocities (wanton murders, amputations and mutilations, gang rapes, sex slavery, vivisections, human experiments--you name it, they did it), they administered conquered territories cruelly, and they treated prisoners of war even more cruelly.
Considering all of the above, conquering the Japanese nation and ensuring their total defeat was not only justified (as I believe you'd agree), it was also entirely proportionate to their warmongering and brutality.
Please stop pushing ahistorical claims.