Xiongnu
Full-scale war broke out in autumn 129 BC, when 40,000 Chinese cavalry made a surprise attack on the Xiongnu at the border markets. In 127 BC, the Han general Wei Qing retook the Ordos. In 121 BC, the Xiongnu suffered another setback when Huo Qubing led a force of light cavalry westward out of Longxi and within six days fought his way through five Xiongnu kingdoms. The Xiongnu Hunye king was forced to surrender with 40,000 men. In 119 BC both Huo and Wei, each leading 50,000 cavalrymen and 100,000 footsoldiers (in order to keep up with the mobility of the Xiongnu, many of the non-cavalry Han soldiers were mobile infantrymen who traveled on horseback but fought on foot), and advancing along different routes, forced the "chanyu" and his court to flee north of the Gobi Desert. Major logistical difficulties limited the duration and long-term continuation of these campaigns. According to the analysis of Yan You (嚴尤), the difficulties were twofold. Firstly there was the problem of supplying food across long distances. Secondly, the weather in the northern Xiongnu lands was difficult for Han soldiers, who could never carry enough fuel. According to official reports, the Xiongnu lost 80,000 to 90,000 men, and out of the 140,000 horses the Han forces had brought into the desert, fewer than 30,000 returned to China.
Xiongnu
Barfield attempted to interpret Xiongnu history as well as narrate it. He made the following points: The Xiongnu confederation was unusually long-lived for a steppe empire. The purpose of raiding China was not simply for goods, but to force the Chinese to pay regular tribute. The power of the Xiongnu ruler was based on his control of Chinese tribute which he used to reward his supporters. The Han and Xiongnu empires rose at the same time because the Xiongnu state depended on Chinese tribute. A major Xiongnu weakness was the custom of lateral succession. If a dead ruler's son was not old enough to take command, power passed to the late ruler's brother. This worked in the first generation but could lead to civil war in the second generation. The first time this happened, in 60 BC, the weaker party adopted what Barfield calls the 'inner frontier strategy.' They moved south and submitted to China and then used Chinese resources to defeat the Northern Xiongnu and re-establish the empire. The second time this happened, about 47 AD, the strategy failed. The southern ruler was unable to defeat the northern ruler and the Xiongnu remained divided.