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.
Donghu people
The (ca. 109–91 BCE) "Shiji" section on Xiongnu history first records the Donghu during the era of Duke Wen of Jin (r. 697–628 BCE) and Duke Mu of Qin (r. ca. 659–621 BCE).At this time Qin and Jin were the most powerful states in China. Duke Wen of Jin expelled the Di barbarians and drove them into the region west of the Yellow River between the Yun and Luo rivers; there they were known as the Red Di and the White Di. Shortly afterwards, Duke Mu of Qin, having obtained the services of You Yu, succeeded in getting the eight barbarian tribes of the west to submit to his authority.
Thus at this time there lived in the region west of Long the Mianzhu, the Hunrong, and the Diyuan tribes. North of Mts. Qi and Liang and the Jing and Qi rivers lived the Yiqu, Dali, Wuzhi, and Quyuan tribes. North of Jin were the Linhu (Forest Barbarians) and the Loufan, while north of Yan lived the Donghu (Eastern Barbarians) and Shanrong (Mountain Barbarians), each of them with their own chieftains. From time to time they would have gatherings of a hundred or so men, but no one tribe was capable of unifying the others under a single rule.