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.
Han–Xiongnu War
In 89 AD, General Dou Xian led a Han expedition against the Northern Xiongnu. The army advanced from Jilu, Manyi, and Guyang in three great columns. In the summer of 89, the forces—comprising a total of 40,000 troops—assembled at Zhuoye Mountain. Near the end of the campaign, Dou's forces chased the Northern Chanyu into the Altai Mountains, killing 13,000 Xiongnu and accepting the surrender of 200,000 Xiongnu from 81 tribes. A light cavalry of 2000 was sent towards the Xiongnu at Hami, capturing the region from them. General Dou Xian marched with his troops in a triumphal progress to the heartland of the Northern Xiongnu's territory and engraved an inscription commemorating the victory on Mount Yanran, before returning to Han. The Han victory in the campaign of 89 AD resulted in the destruction of the Xiongnu state. In 2017, a joint Sino-Mongolian archaeological expedition rediscovered the Inscription of Yanran in the Khangai Mountains of central Mongolia.