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.
Wuhuan
In 209 BC, Modu Chanyu, founder of the Xiongnu empire, defeated the Donghu. The Wuhuan and Xianbei were remnants of the Donghu who had fled east. The Xianbei, of the lateral Donghu line, resided to the north of the Wuhuan. The Wuhuan were of the direct Donghu line and got involved in many relations with the Chinese due to their more southern location (around Liaodong). Until 121 BC, the Wuhuan was a tributary of the Xiongnu empire. The Hou Hanshu (Ch. 120) says: "From the time that Modu Shanyu crushed them the Wuhuan became weak. They were kept in constant subjugation to the Xiongnu and were forced to pay annual taxes of cow, horse and sheep skins. If anybody did not pay this tax his wife and children were taken from him."