This article is an account of Soviet and Mongolian efforts to manipulate a nationalist insurrection in Chinese Altai in 1944–45. For the Soviet leader Joseph Stalin this insurrection, led by a Kazakh nationalist, Osman Batyr, offered an excellent opportunity to attend to Soviet security interests in Xinjiang. For the Prime Minister of the Mongolian People's Republic (MPR), Khorloogiin Choibalsan, Osman represented an important investment in the process of expanding the MPR's regional influence and prestige. Choibalsan intended to co-opt Osman in an expanded Great Mongolia, which he hoped to build up at China's expense by winning the loyalty of the Kazakhs in Xinjiang and the Mongol banners of what is now Inner Mongolia. Stalin supported Choibalsan's vision for a time, until he reached a broader accommodation with China, ending Soviet support for anti-Chinese nationalist movements and putting an end to Choibalsan's Great Mongolia Dream.