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.
Su Wu
In 100 BC, there was a short-lived détente between long-term adversaries the Han and the Xiongnu. One year earlier, in 101 BC, a new chanyu had come to power in Xiongnu, Chanyu Qiedihou (且鞮侯), who had expressed an interest in peace with the Han and who, as a goodwill gesture, had allowed some Han diplomats who had been detained by the Xiongnu to return to Han, along with gifts from the chanyu.