Mongolia was a country in Asia before the Great War. It was to appear in the canceled Fallout Extreme. A band of raiders called the Huns lived in the area.
Before the war, the Gobi Campaign took place here in the Gobi Desert between the US Army and the People's Liberation Army. This raises the possibility that Mongolia, or parts of it, were annexed by China at some point.
The Khans, a raider group originating from Vault 15 in New California in the post-War United States, bases their culture on Mongolian history, such as Genghis Khan and the Mongol Empire.
Mongolia was to appear in Fallout Extreme, and is referenced in Fallout, Fallout 2, and Fallout: New Vegas.