Xiongnu
The Xiongnu () were a confederation of nomadic peoples who, according to ancient Chinese sources, inhabited the eastern Asian Steppe from the 3rd century BC to the late 1st century AD. Chinese sources report that Modu Chanyu, the supreme leader after 209 BC, founded the Xiongnu Empire.
Yuezhi
Gradually the Xiongnu grew stronger and war broke out between them and the Yuezhi. There were at least four wars between the Yuezhi and Xiongnu according to the Chinese accounts. The first war broke out during the reign of the Xiongnu monarch Touman (who died in 209 B.C) who suddenly attacked the Yuezhi. The Yuezhi wanted to kill Modu, the son of the Xiongnu king Touman kept as a hostage to them, but Modu stole a good horse from them and managed to escape to his country. He subsequently killed his father and became ruler of the Xiongnu. It appears that the Xiongnu did not defeat the Yuezhi in this first war. The second war took place in the 7th year of Modu era (203 B.C.). From this war, a large area of the territory originally belonging to the Yuezhi was seized by the Xiongnu and the hegemony of the Yuezhi started to shake. The third war probably was at 176 BC (or shortly earlier) and the Yuezhi were badly defeated.