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.
Jin Midi
Jin Midi was born in 134 BC to a royal Xiongnu family. He was the heir apparent to Xiongnu's Prince of Xiutu, one of the major princes under the supreme ruler of the Xiongnu, the "Chanyu" Gunchen. After Gunchen's death in 126 BC, his brother Ichise succeeded him. During this time, the Prince of Xiutu and another major prince, the Prince of Hunye, were responsible for defending Xiongnu's southwestern border with Han Dynasty – modern central and western Gansu.