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Which of these would make a bigger difference:
Churchill dies some time after September 1940.
Hitler dies some time after December 1941- ie having declared war on the US.
FDR dies after December 7th 1941
Stalin dies after June 22 1941.
I am not sure if there is a Japanese 'leader'. I am guessing it is more likely to to be Tojo than Hirohito, again we are assuming after December 7 1941