The En of Han Dynasty (漢朝末年 or 東漢末年, the End of Eastern Han Dynasty) refers to a period roughly coinciding with the reign of Han Dynasty's final emperor Emperor Xian (r. 189-220) when the empire, with its institutions destroyed by the warlord Dong Zhuo, fractured into regional regimes ruled by various warlords. Eventually, one of those warlords, Cao Cao, was able to gradually reunite the empire, ostensibly under Emperor Xian's rule but in fact under his own -- but Cao's efforts to completely reunify the empire were rebuffed at the Battle of Chibi, where his armies were defeated by those of Sun Quan, paving the way for the Three Kingdoms period. The Han Dynasty finally formally ended in 220 when Cao's heir Cao Pi pressured Emperor Xian into abdicating the throne in his favor, establishing Cao Wei (also known somewhat inaccurately as the Kingdom of Wei); eventually, in response, Liu Bei established Shu Han, while Sun Quan established Eastern Wu, and the three regimes coexisted for decades until each was destroyed by the Jin Dynasty under the Sima clan.