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.
Xiongnu
Coincidentally, the Southern Xiongnu were plagued by natural disasters and misfortunes – in addition to the threat posed by Punu. Consequently, in 50 AD, the Southern Xiongnu submitted to tributary relations with Han China. The system of tribute was considerably tightened by the Han, to keep the Southern Xiongnu under control. The "chanyu" was ordered to establish his court in the Meiji district of Xihe commandery and the Southern Xiongnu were resettled in eight frontier commanderies. At the same time, large numbers of Chinese were also resettled in these commanderies, in mixed Han-Xiongnu settlements.
Economically, the Southern Xiongnu became reliant on trade with the Han.