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.
Huns
Since Joseph de Guignes in the , modern historians have associated the Huns who appeared on the borders of Europe in the with the Xiongnu who had invaded China from the territory of present-day Mongolia between the and the . Due to the devastating defeat by the Chinese Han dynasty, the northern branch of the Xiongnu had retreated north-westward; their descendants may have migrated through Eurasia and consequently they may have some degree of cultural and genetic continuity with the Huns. Scholars also discussed the relationship between the Xungnu, the Huns, and a number of people in central Asia were also known as or came to be identified with the name "Hun" or "Iranian Huns", the Chionites, the Kidarites, and the Hephthalites (or White Huns) being the most prominent.