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.
Emperor Ming of Han
As crown prince, Crown Prince Zhuang was often requested by Emperor Guangwu to render opinions in important matters. In 51, he was involved in making a major correct decision in Han's relationship with Xiongnu. By that point, Xiongnu had a civil war and divided into two—with North Xiongnu ruled by Chanyu Punu (蒲奴) and South Xiongnu ruled by Chanyu Bi (比). Han had become allied with South Xiongnu, and in response, Chanyu Punu, also wanting peace with Han, requested a "heqin" marriage. Prince Zhuang suggested that Emperor Guangwu refuse the proposal, reasoning that North Xiongnu had only made the proposal to alienate South Xiongnu from Han. Emperor Guangwu agreed.