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
In 53 BC Huhanye (呼韓邪) decided to enter into tributary relations with Han China. The original terms insisted on by the Han court were that, first, the "chanyu" or his representatives should come to the capital to pay homage; secondly, the "chanyu" should send a hostage prince; and thirdly, the "chanyu" should present tribute to the Han emperor. The political status of the Xiongnu in the Chinese world order was reduced from that of a "brotherly state" to that of an "outer vassal" (外臣). During this period, however, the Xiongnu maintained political sovereignty and full territorial integrity. The Great Wall of China continued to serve as the line of demarcation between Han and Xiongnu.