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.
History of China
Northern China fragmented into a series of independent kingdoms, most of which were founded by Xiongnu, Xianbei, Jie, Di and Qiang rulers. These non-Han peoples were ancestors of the Turks, Mongols, and Tibetans. Many had, to some extent, been "sinicized" long before their ascent to power. In fact, some of them, notably the Qiang and the Xiongnu, had already been allowed to live in the frontier regions within the Great Wall since late Han times. During the period of the Sixteen Kingdoms, warfare ravaged the north and prompted large-scale Han Chinese migration south to the Yangtze Basin and Delta.