A Japanese attack timed to coincide with Germany's invasion could have forced the Soviet Union to fight on two fronts. That would have been a more direct form of help to Germany than the southern campaign Japan chose. Earlier clashes nevertheless suggest that Japanese ground forces would still have faced serious difficulties against the Soviets. The resulting alignment could have left Britain fighting Germany and Italy and aiding the Soviet Union while remaining outside Japan's northern war.
Chapter · 1:12:47-1:14:11
What a coordinated Japanese attack on the Soviet Union might change
A coordinated northern attack could assist Germany while creating a different pattern of alliances and wars.