We taught the lesson on this, didn't we?
How many people alive today truly remember what it was like during WW2?
I would argue that Germany's invasion of the Soviet Union is actually what did them in, not the US invasion
What about the comments by no less than Admiral Zhukov himself acknowledging that in his view, the USSR couldn't have defeated Germany without US assistance?
But this is all beside the point of extreme nationalism being a bad thing