Thande
Donor
OTL neighbouring Tannu Tuva remained independent from 1924 until its annexation towards the end of WW2; however, that was on the request of the Tannu Tuvan government itself.
During the second world war Mongolia was still de jure a part of the Republic of China, though it had been de facto independent as a Soviet ally since the 1920s; in 1945 Chiang Kai-shek conceded its independence in exchange for Stalin recognising Inner Mongolia as part of China. However, is there any way that the USSR could have annexed Mongolia altogether? I'm guessing this would have to come at the end of WW2 rather than later on - while it would perhaps be more plausible to do so at the time of the Sino-Soviet split, it would probably provoke Cold War confrontations.
During the second world war Mongolia was still de jure a part of the Republic of China, though it had been de facto independent as a Soviet ally since the 1920s; in 1945 Chiang Kai-shek conceded its independence in exchange for Stalin recognising Inner Mongolia as part of China. However, is there any way that the USSR could have annexed Mongolia altogether? I'm guessing this would have to come at the end of WW2 rather than later on - while it would perhaps be more plausible to do so at the time of the Sino-Soviet split, it would probably provoke Cold War confrontations.