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
Due to the many losses inflicted on the Xiongnu, rebellion soon broke out and former enslaved people rose up in arms. Around 80 BC, the Xiongnu attacked the Wusun in a punitive campaign and soon the Wusun monarch requested military support from the Han empire. In 72 BC, the joint forces of the Wusun and Han invaded the territory of the Luli King of the Right. Around 40,000 Xiongnu people and many of their livestock were captured before their city was sacked after the battle. The very next year, various tribes invaded and raided the Xiongnu territory from all fronts; Wusun from the west, Dingling from the north, and Wuhuan from the east. The Han forces had set out in five columns and invaded from the south. According to "Hanshu", this event marks the beginning of Xiongnu decline and the dismantlement of the confederation.