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.
History of Mongolia
During the next century, as Chinese strength waned, border warfare between the Chinese and the Xiongnu was almost incessant. Gradually the nomads forced their way back into Gansu and the northern part of what is now China's Xinjiang. In about the middle of the 1st century AD, a revitalized Eastern Han dynasty (AD 25-220) slowly recovered these territories, driving the Xiongnu back into the Altai Mountains and the steppes north of the Gobi. During the late 1st century AD, having reestablished the administrative control over southern China and northern Vietnam that had been lost briefly at beginning of this same century, the Eastern Han made a concerted effort to reassert dominance over Inner Asia.
The concept of Mongolia as an independent power north of China is seen in the letter sent by Emperor Wen of Han to Laoshang Chanyu in 162 BC (recorded in the Hanshu):
The identity of the ethnic core of Xiongnu has been a subject of varied hypotheses and some scholars, including A.Luvsandendev, , Henry Howorth, Rashpuntsag, Alexey Okladnikov, Peter Pallas, Isaak Schmidt, Nikita Bichurin and Byambyn Rinchen, insisted on a Mongolic origin.