During the Interbellum, Russia sought to extend its influence in Asia as a part of the third Ten-Year Plan. Part of this involved developing links with the mainly Uyghur Muslim region of East Turkestan (known as Sinkiang to the Chinese and termed Dzungaria by the Russians), which had declared independence during the Great War, independence threatened only by the warlords of the area. To encourage the Uyghurs to support Russian colonialism, Tsar Peter V sent a force under Georgiy Zhukov to clear out the bandits and warlords and, being successful, secured a Russo-Dzungar Treaty of Friendship in 1925. From then until 1935 the Russian presence in Central Asia was strengthened, mainly to bolster their vassal khanate in Mongolia, which was threatened by militant Japan and almost just as keenly by Nationalist China (which, to be honest, wasn't head over heels for the Russians in the first place; less so after the 'abduction of Sinkiang').
During the Great Patriotic War (World War Two to everyone else, and plain unfortunate for those who were killed in it) the Russians developed the area even more, using the Uyghur capital of Urumchi as a transit base for troops transferred to and from the Far East to or from the fighting in the Russian heartland. This strengthened the Dzungarian economy and also the naitonalism of the area, assisted by the stationing of soldiers from Muslim Russian Turkestan (Muslims tactfully seen as looking less like colonialism to the 'natives') who brought ideas of the tactics of Kirghiz and Uzbek warriors who had resisted the Russians. This irritated the Chinese who as a part of the Big Five aimed to reclaim Tibet and East Turkestan after they had settled accounts with the Japanese. This was irrelevant: Mao's Communists toppled the Nationalists in 1948, founding their Chinese Soviet Republic and, after exiling opposition to quasi-independent Taiwan (recognised almost instantly as the legitimate China by the Russians, who saw Communists as more dangerous than the Nationalists mainly through their capacity for organisation), turning their attention to 'reclamation of occupied territories' and 'liberation of the peasants and proletariat of the western areas: mere ideological claptrap to the West, but dangerous to war-weary but war-cautious Russians(once-bitten by the Germans, twice shy of everyone). And it was not long before, despite terrible logistics and the fact that both Powers had more pressing needs rebuilding the homeland, an arms race broke out in the middle of nowhere.