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.
Xiongnu
After their previous overlords, the Yuezhi, migrated into Central Asia during the 2nd century BC, the Xiongnu became a dominant power on the steppes of north-east Central Asia, centred on an area known later as Mongolia. The Xiongnu were also active in areas now part of Siberia, Inner Mongolia, Gansu and Xinjiang. Their relations with adjacent Chinese dynasties to the south east were complex, with repeated periods of conflict and intrigue, alternating with exchanges of tribute, trade, and marriage treaties.