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.
Origin of the Huns
The chief piece of evidence linking the Xiongnu to the European and Iranian Huns is the similarity of their names. Supporting evidence is provided by historical records indicating that the term "Xiongnu" was used for the people referred to in Sogdian and Sanskrit texts as the "Xwn" and "Huṇa" respectively, terms used for peoples called Huns in the West. Another important connection is the use of similar metallic cauldrons by the European Huns and the Xiongnu. There remain a number of outstanding differences, however, including generally different archaeological profiles and a wide variety of customs attested among the various Hunnic groups. Additionally, there is a two hundred year gap between the last recorded activities of the Xiongnu and the first appearance of the Huns in Europe and Central Asia. These issues have caused some scholars to reject the identification.