King Zhaoxiang of Qin
In 293 BC, East Zhou decided to ally itself with the states of Han and Wei, and sent troops to help attacking Qin. However, the combined forces of this alliance was destroyed at Yique by the young Qin general Bai Qi, with 240,000 men killed and their commander Gongsun Xi (公孫喜) captured and executed. After this loss, the East Zhou was unable to actively participate in future interstate struggles in any significant fashion.
In 256 BC, Duke Wu of West Zhou (西周武公) allied with other states to stop the Qin offensive on the Han city of Yangcheng. In retaliation, King Zhaoxiang of Qin sent general Jiu to invade West Zhou, successfully breaking into Wangcheng. The Duke Wu was taken to Xianyang to beg for mercy, conceding all his lands. Both King Nan and Duke Wu would die later that year, and the subsequent Duke of West Zhou, Duke Wen (西周文公), was exiled to Danhuju (憚狐聚). Because the Zhou royal court had fallen from power and King Nan had died without a successor, the Eastern Zhou Dynasty collapsed, ending 879 years of Zhou monarchy. The remaining East Zhou state was also conquered by Qin chancellor Lü Buwei seven years later in 249 BC during the reign of King Zhaoxiang's grandson King Zhuangxiang, after Duke Jing of East Zhou attempted to form an anti-Qin alliance with other states.
History of the Han dynasty
The Zhou dynasty (c. 1050–256 BCE) had made the State of Qin in Western China as an outpost to breed horses and act as a defensive buffer against nomadic armies of the Rong, Qiang, and Di peoples. After conquering six Warring States (i.e. Han, Zhao, Wei, Chu, Yan, and Qi) by 221 BCE, the King of Qin, Ying Zheng, unified China under one empire divided into 36 centrally-controlled commanderies. With control over much of China proper, he affirmed his enhanced prestige by taking the unprecedented title "huangdi" (皇帝), or 'emperor', known thereafter as Qin Shi Huang (i.e. the first emperor of Qin). Han-era historians would accuse his regime of employing ruthless methods to preserve his rule.
Qin Shi Huang died of natural causes in 210 BCE. In 209 BCE the conscription officers Chen Sheng and Wu Guang, leading 900 conscripts through the rain, failed to meet an arrival deadline; the "Standard Histories" claim that the Qin punishment for this delay would have been execution. To avoid this, Chen and Wu started a rebellion against Qin, known as the Dazexiang Uprising, but they were thwarted by the Qin general Zhang Han in 208 BCE; both Wu and Chen were subsequently assassinated by their own soldiers. Yet by this point others had rebelled, among them Xiang Yu (d. 202 BCE) and his uncle Xiang Liang (項梁/项梁), men from a leading family of the Chu aristocracy. They were joined by Liu Bang, a man of peasant origin and supervisor of convicts in Pei County. Mi Xin, grandson of King Huai I of Chu, was declared King Huai II of Chu at his powerbase of Pengcheng (modern Xuzhou) with the support of the Xiangs, while other kingdoms soon formed in opposition to Qin. Despite this, in 208 BCE Xiang Liang was killed in a battle with Zhang Han, who subsequently attacked Zhao Xie the King of Zhao at his capital of Handan, forcing him to flee to Julu, which Zhang put under siege. However, the new kingdoms of Chu, Yan, and Qi came to Zhao's aid; Xiang Yu defeated Zhang at Julu and in 207 BCE forced Zhang to surrender.