How was Mongolia during USSR?

Actually it did. Partly. The rest of Mongolia was not annexed because of agreement with Allies. The yellow area is Republic of Tannu-Tuva or just Tuva who is now a part of Russia. read more

During World War II, because of a growing Japanese threat over the border between Mongolia and Manchuria, the Soviet Union reversed the course of Mongolian socialism in favor of a new policy of economic gradualism and build-up of the national defence. read more

In this state it have existed in the period 1921-1944 until Tuva's government requested to become part of the Soviet Union. As for Mongolia proper, it was a part of the Soviet Union in almost everything, but a name. During the Soviet Era it was considered unofficial 16th republic. read more

The two countries had direct links among ministries, agencies, departments, and party organizations. The Soviet Union encouraged direct contacts between Mongolia and the Buryatskaya Autonomous Soviet Socialist Republic and Tuvinskaya Autonomous Soviet Socialist Republics as well as the Central Asian Soviet republics. read more