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.
Turkic migration
Apparently the Xiongnu comprised a number of tribes and geographic groups, not all of which were probably Turkic (considering the later mixed ethnicity). The "Records of the Grand Historian" mention the Mianshu, Hunrong and Diyuan west of Long; the Yiqu, Dali, Wiezhi and Quyan north of the Qi and Liang mountains and Jing and Qi Rivers; the Forest Barbarians and Loufan north of Jin and the Eastern Barbarians and Mountain Barbarians north of Yan. Later the treatise mentions others.