They literally made them a protectorate after fighting a bloody four year war that Japan started. Then denied them the right to field a military so that they wouldn’t start their shit up again.
What was the US supposed to do after Pearl Harbor? Shrug it off?
I find your claims of Japan being undermined by the US to be dubious at best. Japan has done very well since WWII. The US gave them their largest market (when many other Asian imports were blocked) and remains their second highest trading partner after China. They have the third largest economy in the world. That’s not exactly a “vassal.”
Looks, I get it, “US bad” no matter what. But out of all the examples of shitty things the US has done, picking Japan is just silly.