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.
Mongols
After the Donghu were defeated by Xiongnu king Modu Chanyu, the Xianbei and Wuhuan survived as the main remnants of the confederation. Tadun Khan of the Wuhuan (died 207 AD) was the ancestor of the proto-Mongolic Kumo Xi. The Wuhuan are of the direct Donghu royal line and the "New Book of Tang" says that in 209 BCE, Modu Chanyu defeated the Wuhuan instead of using the word Donghu. The Xianbei, however, were of the lateral Donghu line and had a somewhat separate identity, although they shared the same language with the Wuhuan. In 49 CE the Xianbei ruler Bianhe (Bayan Khan?) raided and defeated the Xiongnu, killing 2000, after having received generous gifts from Emperor Guangwu of Han. The Xianbei reached their peak under Tanshihuai Khan (reigned 156–181) who expanded the vast, but short lived, Xianbei state (93–234).