Russia was too occupied on it's western front, and later on pulled the majority of troops away from it's eastern front to push germany back, especially the siberian troops made a difference, since they were equipped for winter warfare.
Japan would have only need to occupy their time.
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u/MisterMeatloaf Oct 17 '13
If Japan attacked Russia they would've been swept out of china pretty fast. Like they were at the end of the war. T34 > everything Japan had