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.
Han–Xiongnu War
When Emperor Wu made the decision to conquer the Hexi Corridor, he had the intention to separate the Xiongnu from the Western Regions and from the Qiang people. In 88 BC, the Xianling tribe of the Qiang people sent an envoy to the Xiongnu, proposing a joint-attack against the Han in the region as they were discontented that they had lost the fertile lands at Jiuquan and Zhangye. It had often been the meeting place between the Xiongnu and the Qiang before the Han empire had conquered and annexed the Hexi Corridor. In 6 BC, Wang Shun (王舜) and Liu Xin noted that the frontier commandaries of Jiuquan, Zhangye, and Dunhuang were established by Emperor Wu to separate the then-powerful Chuoqiang tribe of the Qiang people from the Xiongnu. The Chuoqiang tribe and its king, however, eventually submitted to the Han empire and took part in the campaigns against the Xiongnu.