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.
Battle of Mobei
Furthermore, the loss of control over the fertile southern grassland meant that Xiongnu had to hole up in the cold, barren land of the northern Gobi Desert and Siberia, struggling to survive. As a result, there was a true truce between the Han Dynasty and Xiongnu for seven years, which ended after a Xiongnu raid in 112 BC at Wuyuan. The Xiongnu, however, never recovered to the strength of their past glory days, and would break apart into smaller clans in the coming decades.