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.
Origin of the Huns
There is a gap of about two hundred years between the conquest of the Xiongnu by the Xianbei and their disappearance from Chinese historical records and the appearance of the Huns in Greco-Roman sources. According to the "Book of the Later Han", the final known Xiongnu emperor either disappeared to the west or moved to the territory of the Wusun in modern Kazakhstan in 91. According to the "Wei shu", they then moved further west to around modern Tashkent, where they were defeated by the Xianbei in 153after this, nothing further is recorded about them for twocenturies.
Denis Sinor argued that the origins of the Huns cannot be established beyond what it is said in the work of Roman historian Ammianus Marcellinus: Ammianus said that the Huns dwelled beyond the Sea of Azov next to "the frozen ocean" before they entered Europe, though Sinor does not take "frozen ocean" literally. Both he and Maenchen-Helfen, meanwhile, note that Ammianus refers to the Huns having been "little known", not unknown, before they appeared in 370: they connect this with a mention of a people called the "Khounoi" by the geographer Ptolemy in the mid-second century. Maenchen-Helfen notes, moreover, that the fact that the Huns were not noticed before 370 is not proof that they came from far away, comparing them to the ancient Hungarians: "We know by now that the Magyars (Hungarians) lived for three hundred years practically unnoticed by the Byzantines in the region of the Dnieper, Bug, Dniester, Pruth, and Sereth before they swept over Central Europe very much like the Huns".