Nomadic empire
The Xiongnu were a confederation of nomadic tribes from Central Asia with a ruling class of unknown origin and other subjugated tribes. They lived on the Mongolian Plateau between the 3rd century BC and the 460s AD, their territories including modern day Mongolia, southern Siberia, western Manchuria, and the modern Chinese provinces of Inner Mongolia, Gansu, and Xinjiang. The Xiongnu was the first unified empire of nomadic peoples. Relations between early Chinese dynasties and the Xiongnu were complicated and included military conflict, exchanges of tribute and trade, and marriage treaties. When Emperor Qin Shihuang drove them away from the south of the Yellow River, he built the famous Great Wall to prevent the Xiongnu from coming back.
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.