The Soviets moved 18 divisions and 1700 tanks from the Far East to the Moscow front starting in early November 1941. The Moscow counteroffensive, using these troop, began Dec 5 1941. We were not at war with Japan at the time.
Richard Sorge --maybe the most valuable spy in 200 years-- was a Soviet spy formally working in a job for the Nazis at their Embassy in Tokyo. Of course Japan and Germany were allies, and the Germans were privvy to some of Japan's war plans:
From Tokyo Sorge let Stalin know that he had no reason to fear being attacked by Japan in the East.
For this reason Stalin could release the millions of troops safeguarding his Eastern flank and tranfer them to Stalingrad and other desperately fought for places.
The decision was so great it could have played a critical factor at Stalingrad and the Battle of Kursk, probably massively impacting the whole of WW2.
Awesome! Beat me to it!
The Battle of Khalkhin-Gol had an effect on Japanese thinking also. And Sorge probably factored that into his analysis.
https://en.wikipedia.org/wiki/Battles_of_Khalkhin_Gol
A primary factor in the USSR’s victory over the German invasion was the weather. Hitler had not provided his troops with any cold weather clothing, leaving them to the mercy of the Russian winter.