AHC: World War II Spans 20 Years

Th Sino-Japanese war didn't even officially start until 1937. Also, there's still no way you make it last beyond 1947.
 
Well, inspired by this, perhaps if you had a unified, Axis-aligned China, it would provide a new front of grand strategic proportions, equivalent to Europe all over again. The division of effort by the Allies to cope with an Axis China and Nazi Germany would result in a huge extension of the war (not to mention a sky-darkening cloud of butterflies).
 
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