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
The supposed Old Chinese sound of the first character (匈) has a possible similarity with the name "Hun" in European languages. The second character (奴) appears to have no parallel in Western terminology. Whether the similarity is evidence of kinship or mere coincidence is hard to tell. It could lend credence to the theory that the Huns were in fact descendants of the Northern Xiongnu who migrated westward, or that the Huns were using a name borrowed from the Northern Xiongnu, or that these Xiongnu made up part of the Hun confederation.