Chizhishizhuhou Chanyu
The southern Xiongnu were a branch of the eastern Xiongnu that followed the rebellious pretender Huhanye and in 51-53 BC moved en masse within the Han borders under protection of Chinese. Since the times of Huhanye, the status of the southern Xiongnu was loyal allies of the Han Dynasty. The southern Xiongnu enjoyed material support of the old "heqin" treaty, and in return guarded the Chinese northern borders and participated in the Chinese external and internecine conflicts as long as the Chinese court respected their independence. However, when the Han imperial court attempted to appoint an ineligible for the crown Western Jükü-Prince Yufuluo from ineligible Right Wing as a Chanyu, instead of respecting the traditional election, the southern Xiongnu dissented and elected a lawful alternate Hyuibu Gudu-heu. Later they expelled Yufuluo, who had to seek safety in exile at the Han imperial court.
History of Mongolia
During the next century, as Chinese strength waned, border warfare between the Chinese and the Xiongnu was almost incessant. Gradually the nomads forced their way back into Gansu and the northern part of what is now China's Xinjiang. In about the middle of the 1st century AD, a revitalized Eastern Han dynasty (AD 25-220) slowly recovered these territories, driving the Xiongnu back into the Altai Mountains and the steppes north of the Gobi. During the late 1st century AD, having reestablished the administrative control over southern China and northern Vietnam that had been lost briefly at beginning of this same century, the Eastern Han made a concerted effort to reassert dominance over Inner Asia.
The concept of Mongolia as an independent power north of China is seen in the letter sent by Emperor Wen of Han to Laoshang Chanyu in 162 BC (recorded in the Hanshu):
The identity of the ethnic core of Xiongnu has been a subject of varied hypotheses and some scholars, including A.Luvsandendev, , Henry Howorth, Rashpuntsag, Alexey Okladnikov, Peter Pallas, Isaak Schmidt, Nikita Bichurin and Byambyn Rinchen, insisted on a Mongolic origin.