Soviet-Japanese Border Wars

Khalkhin Gol, 1939. Soviet BT-7 tanks on the offensive.

Date	1932–1939
Location	Mongolia, Primorsky Krai, Manchuria
Result	Soviet and Mongolian victory Soviet–Japanese Neutrality Pact

Belligerents

Soviet Union

Mongolian People's Republic

Empire of Japan

Manchukuo

Commanders and leaders

Georgy Zhukov

Grigory Shtern

Vasili Blyukher

Khorloogiin Choibalsan

Kenkichi Ueda

Yoshijirō Umezu

Michitaro Komatsubara

The Soviet–Japanese border conflicts (also known as the Soviet-Japanese Border War) was a series of battles and skirmishes between the forces of the Union of Soviet Socialist Republics and the Empire of Japan, as well as their respective puppet states of Mongolia and Manchukuo. Lasting from 1932 to 1939, most of the conflicts were small border skirmishes until May 1939, with the notable exception of the Battle of Lake Khasan. The Border War was resolved in a series of engagements at Khalkin-Gol, where the Soviets inflicted a decisive defeat on the Japanese. This resulted in the Soviet-Japanese Neutrality Pact. It should not be confused with the conflict in August 1945 when the Soviet Union declared war in support of the other Allies of World War II and launched the Manchurian Strategic Offensive Operation.

Following the Japanese invasion of Manchuria in 1931, violations of the vaguely defined Manchukuo-Mongolia-USSR border were frequent. Most of these were misunderstandings, but some were intentional acts of espionage. According to the IJA, between 1932 and 1934, 152 border disputes occurred, largely because the Soviets found it necessary to gather intelligence inside Manchuria. For their part, the Soviets blamed the Japanese for 15 cases of border violation, 6 air intrusions, and 20 episodes of "spy smuggling" in 1933 alone. Hundreds more violations were reported by both sides throughout the following years. To make matters worse, Soviet-Japanese diplomacy and trust had declined even further in these years, with the Japanese being openly called "fascist enemies" at the Seventh Comintern Congress in July 1935.

In 1937, the Japanese invaded China, starting the Second Sino-Japanese War. During the first two years of the war, the Soviets heavily aided the Chinese, increasing tensions with Japan. From October 1937 to September 1939, the Soviets supplied the Chinese with 82 tanks, over 1,300 pieces of artillery, over 14,000 machine guns, 50,000 rifles, 1,550 trucks and tractors, and also ammunition, equipment and supplies. They also provided 3,665 military advisors and "volunteers". 195 of these men, almost all officers, died in battle against Japanese forces. Large-scale aid ceased by the end of the Soviet-Japanese border wars.

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