Xiongnu
The Xiongnu () were a confederation of nomadic peoples who, according to ancient Chinese sources, inhabited the eastern Asian Steppe from the 3rd century BC to the late 1st century AD. Chinese sources report that Modu Chanyu, the supreme leader after 209 BC, founded the Xiongnu Empire.
Military history of China before 1911
Armies during the Qin and Han dynasties largely inherited their institutions from the earlier Warring States Period, with the major exception that cavalry forces were becoming more and more important, due to the threat of the Xiongnu. Under Emperor Wu of Han, the Chinese launched a series of massive cavalry expeditions against the Xiongnu, defeating them and conquering much of what is now Northern China, Western China, Mongolia, Central Asia, and Korea. After these victories, Chinese armies were tasked with the goal of holding the new territories against incursions and revolts by peoples such as the Qiang, Xianbei and Xiongnu who had come under Chinese rule.