Xiongnu

Around 209 BCE Modu Chanyu seized power, killed his father, and bound the scattered tribes of the Mongolian and Manchurian grasslands into a single confederation ruled from the centre and split into a left (eastern) and right (western) wing. His army was built on mounted archers, and within a decade it had broken the Donghu and pushed back the Yuezhi. In 200 BCE Modu trapped the founding Han emperor Gaozu and besieged him for seven days near Pingcheng; the Han escaped only by buying peace. For most of a century the Chinese paid the steppe under the heqin policy — annual silk and grain, plus Han princesses sent north as brides, renewed at each new reign — and linked their frontier walls into what became the Great Wall to hold the horsemen off. Emperor Wu of Han abandoned appeasement in 133 BCE and went on the offensive, and after 119 BCE the Xiongnu withdrew north while the Han pushed settlers into the Gansu corridor.

The confederation came apart from within. It split into rival eastern and western lines in the first century BCE, and after 48 CE the Southern Xiongnu submitted to the Eastern Han as vassals and were settled along the frontier, where they served as auxiliaries against their own northern kin. Between 89 and 91 CE a Han–Southern pincer, with the Xianbei attacking from the east, shattered the Northern Xiongnu; the Northern Chanyu was defeated near the Altai and fled west, and the Xianbei took over the steppe in their place. Southern remnants persisted long enough to found short-lived states during the Sixteen Kingdoms in the 4th–5th centuries, but as a distinct power the Xiongnu were gone. They left no writing of their own — their court scribes wrote in Chinese — and their language is unclassified, so almost everything known about them comes from the records of the Han who fought and paid them. The often-repeated link to the European Huns rests on the resemblance of the names; the evidence for it remains controversial and unproven.