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.
Lü Buwei
The "Shiji" mentioned that Lü Buwei had a beautiful "dancing girl", Lady Zhao, in his household, with whom Zichu became so infatuated that he asked for her. Lü Buwei reluctantly presented Lady Zhao to Zichu, and they returned to Handan. In 259 BC, Lady Zhao gave birth to a son, Ying Zheng, who eventually unified China under the Qin Dynasty and became historically known as "Qin Shi Huang" (First Emperor of Qin). After the death of King Zhaoxiang in 251 BC, Lord Anguo was enthroned and became historically known as "King Xiaowen", but he died three days after his coronation in 250 BC. Zichu succeeded his father and became historically known as "King Zhuangxiang". King Zhuangxiang appointed Lü Buwei as his chancellor (相國; or prime minister) and enfeoffed him as "Marquis Wenxin" (文信侯) with a taxable fief covering 100,000 households in Luoyang. While in office, Lü Buwei oversaw Qin's military campaigns against neighbouring states. When King Zhuangxiang died in 247 BC, Ying Zheng (then 13 years old) succeeded him, while Lü Buwei continued serving as a chancellor and regent to the young king.