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.
Shuofang
In the chaos of the rebellions that took place during the end of the Qin Dynasty, the Xiongnu once again moved into the area and took control, and retained this area even after the foundation of the Han Dynasty, using it as an important staging post for raiding into northern and northeastern China. It was only during the Han–Xiongnu War launched by Emperor Wu that the Han Dynasty proactively sought to take over the former borderlands of the Qin Dynasty. In 127 BC, an expedition led by Wei Qing defeated the Xiongnu, leading to the foundation of Shuofang Commandery; by 8 BC the commandery had ten constituent counties.