Japan was certainly no match for the Soviets in the state they were in. But if they had ended the war in China and threw the whole weight of the Kwantung Army into the East, Stalin would have had a problem. Of course even then, I don't think Japan could have made serious gains, as TA Garnder has already pointed out there was little to gain in the Soviet Far East.

Much more substantian is the delay of US entry into the war, as it would have positively impacted Germany's effort in Russia. Add to that with the full weight of the Japanese Army invoved against Russia, they would have to withdraw some forces from the West.

This all supposes, though, Japan ended the war in China. There would be no other way to carry out an assault against the Soviets and hope for it not to have drastic and terrible consequences within a year.

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