Nomadic empire
The Xiongnu were a confederation of nomadic tribes from Central Asia with a ruling class of unknown origin and other subjugated tribes. They lived on the Mongolian Plateau between the 3rd century BC and the 460s AD, their territories including modern day Mongolia, southern Siberia, western Manchuria, and the modern Chinese provinces of Inner Mongolia, Gansu, and Xinjiang. The Xiongnu was the first unified empire of nomadic peoples. Relations between early Chinese dynasties and the Xiongnu were complicated and included military conflict, exchanges of tribute and trade, and marriage treaties. When Emperor Qin Shihuang drove them away from the south of the Yellow River, he built the famous Great Wall to prevent the Xiongnu from coming back.
Han–Xiongnu War
As the Xiongnu economic and military situation deteriorated, the Xiongnu were willing to renew peace during the reigns of Huyandi Chanyu (r. 85-69 BC) and Xulüquanqu Chanyu (r. 68-60 BC), but the Han court gave only one option, tributary submission. After Xulüquanqu Chanyu's death in 60 BC, a Xiongnu civil war broke loose in 57 BC over the succession, which fully fragmented the Xiongnu confederation with many contenders. In the end, only Zhizhi Chanyu and Huhanye Chanyu survived the struggle to power. After Zhizhi Chanyu (r. 56–36 BC) had inflicted serious losses against his rival Huhanye Chanyu (r. 58–31 BC), Huhanye and his supporters debated whether to request military protection and become a Han vassal. In 53 BC, Huhanye decided to do so and surrendered to the reign of the Han empire.