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.
Xunyu
Chinese annals contain a number of references to the "Xunyu". The earliest authors were Sima Qian (c. 145 or 135 BC – 86 BC), Ying Shao (AD 140-206), Wei Zhao (204-273), and Jin Zhuo (c. late 3rd or 4th century). Without citing any arguments, they claimed that "Xunyu" or "Xianyun" were names that designated nomadic people who during the Han dynasty were called "Xiongnu" (匈奴). That view was also held by the Tang dynasty commentator Sima Zhen (c. 8th century).