History of Mongolia
Although the Xiongnu finally had been split into two parts in AD 48, the Xianbei (or Hsien-pei in Wade–Giles) had moved (apparently from the east) into the region vacated by the Xiongnu. The Xianbei were the northern branch of the Donghu (or Tung Hu, the Eastern Hu), a proto-Mongol group mentioned in Chinese histories as existing as early as the 4th century BC. The language of the Donghu is believed to be proto-Mongolic to modern scholars. The Donghu were among the first peoples conquered by the Xiongnu. Once the Xiongnu state weakened, however, the Donghu rebelled. By the 1st century AD, two major subdivisions of the Donghu had developed: the proto-Mongolic Xianbei in the north and the Wuhuan in the south.
Xiongnu
Ancient China often came in contact with the Xianyun and the Xirong nomadic peoples. In later Chinese historiography, some groups of these peoples were believed to be the possible progenitors of the Xiongnu people. These nomadic people often had repeated military confrontations with the Shang and especially the Zhou, who often conquered and enslaved the nomads in an expansion drift. During the Warring States period, the armies from the Qin, Zhao, and Yan states were encroaching and conquering various nomadic territories that were inhabited by the Xiongnu and other Hu peoples.