<Tr> <Th_colspan="2"> Standard Mandarin </Th> </Tr> <Tr> <Th> Hanyu Pinyin </Th> <Td> Dōnghàn Mònián </Td> </Tr> <P> The end of the Han dynasty refers to the period of Chinese history from 189 to 220 AD, which roughly coincides with the tumultuous reign of the Han dynasty's last ruler, Emperor Xian . During this period, the country was thrown into turmoil by the Yellow Turban Rebellion (184 - 205). Meanwhile, the Han Empire's institutions were destroyed by the warlord Dong Zhuo, and fractured into regional regimes ruled by various warlords, some of whom were nobles and officials of the Han imperial court . Eventually, one of those warlords, Cao Cao, was able to gradually reunify the empire, ostensibly under Emperor Xian's rule, but the empire was actually controlled by Cao Cao himself . Cao Cao's efforts to completely reunite the Han empire were rebuffed at the Battle of Red Cliffs in 208 / 209, when his armies were defeated by the allied forces of Sun Quan and Liu Bei . The Han dynasty formally ended in 220 when Cao Cao's son and heir, Cao Pi, pressured Emperor Xian into abdicating in his favour . Cao Pi became the emperor of a new state, Cao Wei . A year later, in response to Cao Pi's usurpation of the Han throne, Liu Bei declared himself emperor of Shu Han; and in 229, Sun Quan followed suit, declaring himself emperor of Eastern Wu . The period from Emperor Xian's abdication in 220 to the partial reunification of China under the Jin dynasty in 265 was known as the Three Kingdoms era in Chinese history . </P> <Table> <Tr> <Th_colspan="2"> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> Conflicts at the end of the Han dynasty </Th> </Tr> <Tr> <Td_colspan="2"> <Ul> <Li> Yellow Turbans </Li> <Li> Liang Province </Li> <Li> Dong Zhuo (Xingyang) </Li> <Li> Yangcheng </Li> <Li> Jieqiao </Li> <Li> Xiangyang </Li> <Li> Fengqiu </Li> <Li> Xu Province </Li> <Li> Yan Province </Li> <Li> Jiangdong </Li> <Li> Cao Cao vs. Zhang Xiu </Li> <Li> Xiapi </Li> <Li> Yijing </Li> <Li> Yuan Shu </Li> <Li> Guandu </Li> <Li> Bowang </Li> <Li> Xiakou </Li> <Li> Northern China (Liyang * Ye * Nanpi * White Wolf Mtn .) </Li> <Li> Jiangxia </Li> <Li> Red Cliffs </Li> <Li> Northwest China (Tong Pass * Jicheng * Lucheng * Qi Mtns . * Yangping) </Li> <Li> Ruxu (213) </Li> <Li> Yi Province </Li> <Li> Hanzhong </Li> <Li> Xiaoyao Ford </Li> <Li> Ruxu (217) </Li> <Li> Fancheng </Li> <Li> Jing Province </Li> <Li> Three Kingdoms → </Li> </Ul> </Td> </Tr> </Table>

Reasons for the collapse of the han dynasty
find me the text answering this question