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.
Huns
Recent scholarship, particularly by Hyun Jin Kim and Etienne de la Vaissière, has revived the hypothesis that the Huns and the Xiongnu are one and the same. De la Vaissière argues that ancient Chinese and Indian sources used "Xiongnu" and "Hun" to translate each other, and that the various "Iranian Huns" were similarly identified with the Xiongnu. Kim believes that the term Hun was "not primarily an ethnic group, but a political category" and argues for a fundamental political and cultural continuity between the Xiongnu and the European Huns, as well as between the Xiongnu and the "Iranian Huns".