Noin-Ula burial site
Many immigrants lived in the Xiongnu pasturelands, but at first they did not mix with the Xiongnu. To be a Xiongnu, one had to be a member of a clan, born of Xiongnu parents. The newcomers were well off, but were outsiders, and could marry only among themselves, not the Xiongnu. Only later did they intermix, increase in numbers, even created a state that existed from 318 to 350 AD.
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.