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.
Turkic peoples
It has often been suggested that the Xiongnu, mentioned in Han Dynasty records, were Proto-Turkic speakers. Although little is known for certain about the Xiongnu language(s), it seems likely that at least a considerable part of Xiongnu tribes spoke a Turkic language. However, some scholars see a possible connection with the Iranian-speaking Sakas. Some scholars believe they were probably a confederation of various ethnic and linguistic groups. Genetics research in 2003 on skeletons from 2000 year old Xiongnu necropolis in Mongolia found some individuals with DNA sequences also present in some modern-day Turks, suggesting that a Turkish component had emerged in the Xiongnu tribe at the end of the Xiongnu period.