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 318, after suppressing a coup by a powerful minister in the Xiongnu-Han court, in which the emperor and a large proportion of the aristocracy were massacred), the Xiongnu prince Liu Yao moved the Xiongnu-Han capital from Pingyang to Chang'an and renamed the dynasty as Zhao (Liu Yuan had declared the empire's name Han to create a linkage with Han Dynasty—to which he claimed he was a descendant, through a princess, but Liu Yao felt that it was time to end the linkage with Han and explicitly restore the linkage to the great Xiongnu chanyu Maodun, and therefore decided to change the name of the state. (However, this was not a break from Liu Yuan, as he continued to honor Liu Yuan and Liu Cong posthumously; it is hence known to historians collectively as Han Zhao).