The Battles of Khalkhin Gol were the decisive engagements of the undeclared Soviet–Japanese border conflicts fought among the Soviet Union, Mongolia, Japan and Manchukuo in 1939. The conflict was named after the river Khalkhin Gol, which passes through the battlefield.
The battle was fought between the Soviet Union and Mongolia on one hand, and Japan on the other. It was fought in Manchuria, located in the north east of China. It lasted from 11 May 1939 to 16 September 1939.
The Soviets and Mongolians won the battles. That battle came before World War II, another war where Soviets and Japanese fought against each other.