6. Although technically preceding the Second World War at the start, the Battles of Khalkhyn Gol were a series of precursor border conflicts in the weeks prior to the invasion of Poland between the Soviet Union and the Empire of Japan
After the Japanese occupation of Manchuria in 1931, the expansionist Pacific Empire increasingly turned its attention towards bordering Soviet territories. First clashing in 1938, the puppet state of Manchukuo was occupied by the Kwantung Army of Japan, comprising many of the finest professional soldiers available, whom on May 11, 1939, engaged a Mongolian cavalry unit in a skirmish. Following the incident, both the Soviets and Japanese dramatically increased their forces in the area, with the Soviets also dispatching Zhukov to serve as commander. Striking first on June 27, without prior authorization from Tokyo, the Japanese attacked a Soviet airbase at Tamsak-Bulak.
Escalating into a full-scale assault, the Japanese initially succeeded in crossing the Khalkhyn Gol – a river separating the primary battlefield – but Zhukov mounted a counter-offensive to push the enemy back on July 5. Sparring back and forth for weeks, with both sides suffering heavy casualties, the battle entered into a prolonged stalemate. Finally, with the war in Europe imminent, Zhukov launched a major offensive designed to end the conflict on August 20. Devastating the Japanese with a sudden aerial and armored attack, the Soviets, having pushed back the invaders, quickly signed a ceasefire on September 15 – two days before the Soviet invasion of Poland.