End of the Han dynasty
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.
Han dynasty
The Xiongnu, a nomadic steppe confederation, defeated the Han in 200 BC and forced the Han to submit as a "de facto" inferior and vassal partner, but continued their military raids on the Han borders. Emperor Wu launched several military campaigns against them. The ultimate Han victory in these wars eventually forced the Xiongnu to accept vassal status as Han tributaries. These campaigns expanded Han sovereignty into the Tarim Basin of Central Asia, divided the Xiongnu into two separate confederations, and helped establish the vast trade network known as the Silk Road, which reached as far as the Mediterranean world. The territories north of Han's borders were quickly overrun by the nomadic Xianbei confederation. Emperor Wu also launched successful military expeditions in the south, annexing Nanyue in 111 BC and Dian in 109 BC, and in the Korean Peninsula where the Xuantu and Lelang Commanderies were established in 108 BC. After 92 AD, the palace eunuchs increasingly involved themselves in court politics, engaging in violent power struggles between the various consort clans of the empresses and empresses dowager, causing the Han's ultimate downfall. Imperial authority was also seriously challenged by large Daoist religious societies which instigated the Yellow Turban Rebellion and the Five Pecks of Rice Rebellion. Following the death of Emperor Ling (r. 168–189 AD), the palace eunuchs suffered wholesale massacre by military officers, allowing members of the aristocracy and military governors to become warlords and divide the empire. When Cao Pi, King of Wei, usurped the throne from Emperor Xian, the Han dynasty ceased to exist.