Under the then unknown Georgy Zhukov, the Soviets won a crushing victory at the battle of Khalkhin Gol (known in Japan as the Nomonhan Incident).
Defeat persuaded the Japanese to expand into the Pacific, where they saw the United States as a weaker opponent than the Soviet Union. If the Japanese had not lost at Khalkhin Gol, they may never have attacked Pearl Harbor.
The Japanese decision to expand southwards also meant that, the Soviets could mass their troops against the threat of Nazi Germany in the West, instead of having to fight on two fronts.
In terms of its strategic impact, the battle of Khalkhin Gol was one of the most decisive battles of the Second World War, but no-one has ever heard of it. Why?, asks Andy Young on Siberian Light.