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Let's say that due to different circumstances, instead of turning into Naziism post-Versailles, Germany underwent the Communist Revolution and turned into a Communist Nation. Same with China during the Warlord period, let's say that due to Soviet support, Mao seized power in China early on and turned them into yet another communist Nation (Manchuria is still in Japanese hands at the start tho).
Then somehow, the alternate International Politburo of the Communists decide that it was time to start a Worldwide War against non-Communists.
Of course, to drag the US into the war, the Communist International ends up trying to use sabotages and agitating US workers to revolt during the Great Depression, or the assassination of FDR equivalent, whatever is easier to achieve.
So, the Communists are:
* Germany
* the Soviet Union
* China
Fighting against:
* Britain
* France
* Italy
* Japan
* USA
...
Which side is more likely to win the war? Consider that now the Communists have German Tech, Soviet Industry, and Chinese Population, aside from the agitation of workers and backing anticolonialist movements everywhere.
No, there is no making separate wars by defeating colonialists one by one before moving into US. In fact, US would be the most furious with their anti-capitalist agitation from the start (having suffered failed communist revolt in 1930s)