The Sino-Soviet Non-Aggression Pact (traditional Chinese: 中蘇互不侵犯條約; simplified Chinese: 中苏互不侵犯条约; pinyin: Zhōng-sū hù bù qīnfàn tiáoyuē) was signed in Nanjing on August 21, 1937, between the Republic of China and the Soviet Union during the Second Sino-Japanese War. It went into effect on the day it was signed. It was registered in League of Nations Treaty Series on September 8, 1937.
At first the treaty led to improving relations between the Kuomintang, Chiang Kai-shek's government and the USSR. Following the signing of the pact, the Soviet Union began sending aircraft to the Chinese national government in Operation Zet, as well as economic aid to help stave off Japanese occupation. Chiang hoped this was a precursor to Soviet intervention into the war, however as time passed he soon realized that the USSR was constricted in what aid it could actually provide, due to not wanting to upset the tacit alliance with Britain, France, and later the United States, who favored China in the war but, would back Japan against the USSR in order to weaken both.
The treaty also allowed the USSR to focus its attention more on the Western border where Nazi Germany was building up for what appeared to be war with the USSR especially after the Soviet-Japanese Neutrality Pact was signed. The pact contributed to the worsening relationship between China and Nazi Germany, which culminated in the end of German military assistance in China.
Ironically, in 1937, while the pact was being signed, the Soviets brazenly breached it before and after the signing, conducting the Xinjiang War (1937) from August to October.
The Soviet Army was assisting its puppet Governor Sheng Shicai in Xinjiang. The Kuomintang Muslim General Ma Hushan led the 36th Division (National Revolutionary Army) to resist the invasion.
Before the invasion, Ma Hushan had communicated with Chiang Kaishek, and he mentioned to Peter Fleming that Chiang was going to send help to fight the Soviets. However, the outbreak of war with Japan led Ma Hushan to face the Soviet Invasion on his own, despite resisting and killing Russian soldiers, Ma Hushan's forces eventually succumbed to Soviet mustard gas bombardment, and Ma Hushan fled to India, where he took a steamer back to China.
Sheng Shicai then invited Soviet forces to garrison in Turfan, right next to Gansu province.
The Republic of China government was fully aware of the Soviet invasion of Xinjiang province, and Soviet troops moving around Xinjiang and Gansu, but was forced to mask these maneuvers to the public as "Japanese propaganda" to avoid an international incident and for continued military supplies from the Soviets.
The Chinese government responded with its own military moves. The Muslim General Ma Buqing was in virtual control of the Gansu corridor at this time. Ma Buqing had earlier fought against the Japanese, but since the Soviet threat was great, Chiang made some arrangements regarding Ma's position. In July 1942 Chiang Kai-shek instructed Ma Buqing to move 30,000 of his troops to the Tsaidam marsh in the Qaidam Basin of Qinghai. Chiang named Ma Reclamation Commissioner, to threaten Sheng Shicai's southern flank in Xinjiang, which bordered Tsaidam.
After Ma evacuated his positions in Gansu, Kuomintang troops from central China flooded the area, and infiltrated Soviet occupied Xinjiang, gradually reclaiming it and forcing Sheng Shicai to break with the Soviets.
The Ili Rebellion broke out in Xinjiang when the Kuomintang Chinese Muslim Officer Liu Bin-Di was killed while fighting Turkic Uyghur Rebels in November 1944. The Soviet Union supported the Turkic rebels against the Kuomintang, and Kuomintang forces were fighting back.
The Kuomintang Chinese government ordered Muslim General Ma Bufang several times to march his troops into Xinjiang to intimidate the pro Soviet Governor Sheng Shicai. This helped provide protection for Chinese settling in Xinjiang. Ma Bufang was sent with his Muslim Cavalry to Urumqi by the Kuomintang in 1945 during the Ili Rebellion to protect it from the Uyghur army from Hi (name for Ili at that time).