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.
Xubu
The Xubu () was a tribe of the Xiongnu confederation that flourished between 3rd century BCE to 4th century CE. Chinese annals noted that the Xubu tribe replaced the Huyan tribe, which was an earlier maternal dynastic tribe of the dynastic union with the paternal dynastic tribe Luandi. The traditional system of conjugal unions is a form of the nomadic exogamic society. The male members of the maternal dynastic line were not eligible for the Chanyu throne, only the male members of the Luandi line, whose father was a Luanti Chanyu, and mother was a Xubu Khatun (Queen) were eligible for the supreme throne. A Xubu could only become a Chanyu after a palace coup.