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.
Xiongnu
An early reference to the Xiongnu was by the Han dynasty historian Sima Qian who wrote about the Xiongnu in the "Records of the Grand Historian" ( BC), drawing a distinct line between the settled Huaxia people (Chinese) to the pastoral nomads (Xiongnu), characterizing it as two polar groups in the sense of a civilization versus an uncivilized society: the Hua–Yi distinction. Pre-Han sources often classify the Xiongnu as a "Hu" people, which was a blanket term for nomadic people in general; it only became an ethnonym for the Xiongnu during the Han.