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 migration
Qin's campaign against the Xiongnu of 215 BCE kept the Xiongnu at bay, driving them out of and seizing the Ordos region. Problems re-emerged after the Qin Dynasty. The Xiong-nu attacked Shanxi of the Han in 201 BCE. Emperor Gaozu of Han bought them off with jade, silk and a Chinese wife for the Shanyu, or leader. Relations with the Xiongnu continued to be troubled and in 133 BC Emperor Wu of Han proceeded against them with 300,000 men. Eighty-one years and fourteen expeditions later in 52 BC the southern Xiongnu surrendered and the northern desisted from raiding. The Han Dynasty military expeditions continued near the frontier of China, in the Han–Xiongnu War, and in 89 AD the Xiongnu state was defeated and soon ended.