Short answers, pulled from the story.
The Battles of Khalkhin Gol were a series of decisive military engagements in 1939 between the Soviet Union and Mongolia on one side and Japan and its Manchurian puppet state Manchukuo on the other. The conflict centered on a disputed border along the Khalkhin Gol river in what is now eastern Mongolia. The Soviet Union, led by General Georgy Zhukov, won a decisive victory using a three-pronged combined-arms offensive.
Georgy Zhukov was a Soviet general who arrived at Khalkhin Gol on the 5th of June 1939 as the new corps commander. He organized a fleet of 2,600 trucks to supply his army 748 kilometers from its base and pioneered a double-envelopment tactic that trapped the Japanese 23rd Infantry Division. The victory earned him the first of his four Hero of the Soviet Union awards.
The Japanese defeat at Khalkhin Gol helped shift imperial strategy away from the Hokushin-ron (strike north against the Soviet Union) toward the Nanshin-ron (strike south into Southeast Asia). Colonel Masanobu Tsuji, who helped instigate the Nomonhan incident, became a leading advocate for attacking Pearl Harbor, and later wrote that witnessing Soviet firepower at Nomonhan convinced him not to support an attack on the Soviet Union in 1941. Japan attacked Pearl Harbor on the 7th of December 1941.
Japanese records reported approximately 20,000 battle and non-battle casualties and 162 aircraft lost in combat. Soviet figures were revised multiple times; a 2001 edition of Krivosheev's study gave totals of 9,703 dead and missing, 15,251 wounded, and 701 sick, for 25,655 total personnel losses. The Soviets also lost 253 tanks, 250 aircraft, and 133 armored cars.
Zhukov used the same double-envelopment structure at Stalingrad's Operation Uranus that he had tested at Khalkhin Gol: fix the enemy in the center, build up a concealed mass force in the rear, then launch pincer attacks on both wings to encircle the opposing army. The tactic trapped the German army at Stalingrad just as it had trapped the Japanese 23rd Infantry Division on the Mongolian steppe.
The main commemorations are in Mongolia. The town of Choibalsan in Dornod Province hosts a museum dedicated to Zhukov and the 1939 battle, while Ulaanbaatar has a second Zhukov museum opened on the 19th of August 1979. The 80th anniversary in 2019 included a military parade in Choibalsan and a concert by the Russian Alexandrov Ensemble on Sukhbaatar Square. The presidents of Russia and Mongolia have jointly attended anniversary ceremonies including the 85th in 2024.