You've already skewed the analysis. It was not at all clear in 1940 that the US would become the arsenal of democracy. The US might also have changed its plan in 1943 and elected to negotiate with the Germans. (I suspect we were in a fight to the end with the Japanese after Pearl Harbor, but that same level of animosity was not as present WRT Germany--ulike in WWI.)
Again this only became inevitable after the end of the period of Fabian delay, and the Roman decision to invade Tunisia. After Cannhae or Lake Trasimene, I do not think the outcome was so inevitable.
Nor can you assume that the aims of those on either side of the playing field won't also change, in either a rational or less than rational way. This latter was my main point.
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