Why is there no history about Outer Mongolia in the history books?

The National Government recognized the independence of Outer Mongolia. When the Qing Dynasty perished, there was no province in Outer Mongolia. Moreover, the Qing dynasty banned Han Chinese from immigrating to Mongolia. The whole outer Mongolia Han people are scarce. Weak countries can migrate to real borders, and the Northeast is an example. But the Qing dynasty made a mistake. Finally, due to the weak national strength and the support of the Soviet Union, there were few Han Chinese in outer Mongolia, and outer Mongolia became independent. If Mongolia has1100,000 Han people, it is impossible for Mongolia to be independent, even with the support of two Soviets.