Han dynasty
To the north of China proper, the nomadic Xiongnu chieftain Modu Chanyu (r. 209–174 BC) conquered various tribes inhabiting the eastern portion of the Eurasian Steppe. By the end of his reign, he controlled Manchuria, Mongolia, and the Tarim Basin, subjugating over twenty states east of Samarkand. Emperor Gaozu was troubled about the abundant Han-manufactured iron weapons traded to the Xiongnu along the northern borders, and he established a trade embargo against the group. In retaliation, the Xiongnu invaded what is now Shanxi province, where they defeated the Han forces at Baideng in 200 BC. After negotiations, the "heqin" agreement in 198 BC nominally held the leaders of the Xiongnu and the Han as equal partners in a royal marriage alliance, but the Han were forced to send large amounts of tribute items such as silk clothes, food, and wine to the Xiongnu.
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.