Nomadic empire
The Xiongnu were a confederation of nomadic tribes from Central Asia with a ruling class of unknown origin and other subjugated tribes. They lived on the Mongolian Plateau between the 3rd century BC and the 460s AD, their territories including modern day Mongolia, southern Siberia, western Manchuria, and the modern Chinese provinces of Inner Mongolia, Gansu, and Xinjiang. The Xiongnu was the first unified empire of nomadic peoples. Relations between early Chinese dynasties and the Xiongnu were complicated and included military conflict, exchanges of tribute and trade, and marriage treaties. When Emperor Qin Shihuang drove them away from the south of the Yellow River, he built the famous Great Wall to prevent the Xiongnu from coming back.
Han–Xiongnu War
The Southern Xiongnu—who had been situated in the Ordos region since about 50 AD—remained within the territory of the Han empire as semi-independent tributaries. They were dependent to the Han empire for their livelihood as indicated by a memorial from the Southern Chanyu to the Han court in 88 AD. Following the military successes against the Xiongnu, General Ban Chao was promoted to the position of Protector General and stationed in Kucha in 91 AD. At the remote frontier, Ban Chao reaffirmed absolute Han control over the Western Regions from 91 AD onwards.