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.
Xianyun
Later Chinese annals contain a number of references to the Xianyun, such as by Sima Qian (c. 145/135 – 86 BCE), Ying Shao (140-206 CE), Wei Zhao (204-273 CE), and Jin Zhuo (late 3rd–4th century CE). Without giving specific arguments, they stated that Xunyu (獯鬻) or "Xianyun" were terms that designated nomadic people who later during the Han dynasty were transcribed as "Xiongnu" (匈奴). This view was also held by the Tang dynasty commentator Sima Zhen (c. 8th century CE). Wang Guowei (1877–1927), as a result of phonetical studies and comparisons based on the inscriptions on bronze and the structure of the characters, came to the conclusion that the tribal names "Guifang" (鬼方), "Xunyu" (獯鬻), "Xianyu" (鮮虞), Xianyun, "Rong" (戎), "Di" (狄), and "Hu" (胡) given in the annals designated one and the same people, who later entered history under the name Xiongnu.