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
As a result of these battles, the Chinese controlled the strategic region from the Ordos and Gansu corridor to Lop Nor. They succeeded in separating the Xiongnu from the Qiang peoples to the south, and also gained direct access to the Western Regions. Because of strong Chinese control over the Xiongnu, the Xiongnu became unstable and were no longer a threat to the Han Chinese.
Ban Chao, Protector General (都護; "Duhu") of the Han dynasty, embarked with an army of 70,000 men in a campaign against the Xiongnu insurgents who were harassing the trade route now known as the Silk Road. His successful military campaign saw the subjugation of one Xiongnu tribe after another. Ban Chao also sent an envoy named Gan Ying to Daqin (Rome). Ban Chao was created the Marquess of Dingyuan (定遠侯, i.e., "the Marquess who stabilized faraway places") for his services to the Han Empire and returned to the capital Luoyang at the age of 70 years and died there in the year 102. Following his death, the power of the Xiongnu in the Western Regions increased again, and the emperors of subsequent dynasties were never again able to reach so far to the west.