assembled an expeditionary force that defeated him at the Battle of Zhizhi and sent his head as a trophy to Chang'an. Tributary relations were discontinued during the reign of Huduershi (18 AD–48), corresponding to the political upheavals of the Xin Dynasty. The Xiongnu took the opportunity to regain control of the western regions, as well as neighboring peoples such as the Wuhuan. In 24 AD, Hudershi even talked about reversing the tributary system. Southern Xiongnu and Northern Xiongnu The Xiongnu's new power was met with a policy of appeasement by Emperor Guangwu. At the height of his power, Huduershi even compared himself to his illustrious ancestor, Modu. Due to growing regionalism among the Xiongnu, however, Huduershi was never able to establish unquestioned authority. In contravention of a principle of fraternal succession established by Huhanye, Huduershi designated his son Punu as heir-apparent. However, as the eldest son of the preceding chanyu, Bi (Pi)—the Rizhu King of the Right—had a more legitimate claim. Consequently, Bi refused to attend the annual meeting at the chanyus court. Nevertheless, in 46 AD, Punu ascended the throne. In 48 AD, a confederation of eight Xiongnu tribes in Bi's power base in the south, with a military force totalling 40,000 to 50,000 men, seceded from Punu's kingdom and acclaimed Bi as chanyu. This kingdom became known as the Southern Xiongnu. Northern Xiongnu The rump kingdom under Punu, around the Orkhon (modern north central Mongolia) became known as the Northern Xiongnu. Punu, who became known as the Northern Chanyu, began to put military pressure on the Southern Xiongnu. In 49 AD, Tsi Yung, a Han governor of Liaodong, allied with the Wuhuan and Xianbei, attacked the Northern Xiongnu. The Northern Xiongnu suffered two major defeats: one at the hands of the Xianbei in 85 AD, and by the Han during the Battle of Ikh Bayan, in 89 AD. The northern chanyu fled to the north-west with his subjects. In about 155 AD, the Northern Xiongnu were decisively "crushed and subjugated" by the Xianbei. According to the fifth-century Book of Wei, the remnants of Northern Chanyu's tribe settled as Yueban (悅般), near Kucha and subjugated the Wusun; while the rest fled across the Altai mountains towards Kangju in Transoxania. It states that this group later became the Hephthalites. Southern Xiongnu Coincidentally, the Southern Xiongnu were plagued by natural disasters and misfortunes—in addition to the threat posed by Punu. Consequently,