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.
Han–Xiongnu War
The Southern Xiongnu—who had been situated in the Ordos region since about 50 AD—remained within the territory of the Han empire as semi-independent tributaries. They were dependent to the Han empire for their livelihood as indicated by a memorial from the Southern Chanyu to the Han court in 88 AD. Following the military successes against the Xiongnu, General Ban Chao was promoted to the position of Protector General and stationed in Kucha in 91 AD. At the remote frontier, Ban Chao reaffirmed absolute Han control over the Western Regions from 91 AD onwards.