Xiongnu
Sinologist Edwin Pulleyblank argued that the Xiongnu were part of a Xirong group called Yiqu, who had lived in Shaanbei and had been influenced by China for centuries, before they were driven out by the Qin dynasty. Qin's campaign against the Xiongnu expanded Qin's territory at the expense of the Xiongnu. In 215 BC, Qin Shi Huang sent General Meng Tian to conquer the Xiongnu and drive them from the Ordos Loop, which he did later that year. After the catastrophic defeat at the hands of Meng Tian, the Xiongnu leader Touman was forced to flee far into the Mongolian Plateau. The Qin empire became a threat to the Xiongnu, which ultimately led to the reorganization of the many tribes into a confederacy.In 209 BC, three years before the founding of Han China, the Xiongnu were brought together in a powerful confederation under a new chanyu, Modu Chanyu. This new political unity transformed them into a more formidable state by enabling formation of larger armies and the ability to exercise better strategic coordination. The Xiongnu adopted many of the Chinese agriculture techniques such as slave labor for heavy labor, wore silk like the Chinese, and lived in Chinese-style homes. The reason for creating the confederation remains unclear. Suggestions include the need for a stronger state to deal with the Qin unification of China that resulted in a loss of the Ordos region at the hands of Meng Tian or the political crisis that overtook the Xiongnu in 215 BC when Qin armies evicted them from their pastures on the Yellow River.
Wuhuan
In 209 BC, Modu Chanyu, founder of the Xiongnu empire, defeated the Donghu. The Wuhuan and Xianbei were remnants of the Donghu who had fled east. The Xianbei, of the lateral Donghu line, resided to the north of the Wuhuan. The Wuhuan were of the direct Donghu line and got involved in many relations with the Chinese due to their more southern location (around Liaodong). Until 121 BC, the Wuhuan was a tributary of the Xiongnu empire. The Hou Hanshu (Ch. 120) says: "From the time that Modu Shanyu crushed them the Wuhuan became weak. They were kept in constant subjugation to the Xiongnu and were forced to pay annual taxes of cow, horse and sheep skins. If anybody did not pay this tax his wife and children were taken from him."