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.
Warring States period
In 265 King Zhaoxiang of Qin made the first move by attacking the weak state of Han which held the Yellow River gateway into Qin. He moved northeast across Wei territory to cut off the Han exclave of Shangdang north of Luoyang and south of Zhao. The Han king agreed to surrender Shangdang, but the local governor refused and presented it to King Xiaocheng of Zhao. Zhao sent out Lian Po who based his armies at Changping and Qin sent out general Wang He. Lian Po was too wise to risk a decisive battle with the Qin army and remained inside his fortifications. Qin could not break through and the armies were locked in stalemate for three years. The Zhao king decided that Lian Po was not aggressive enough and sent out Zhao Kuo who promised a decisive battle. At the same time Qin secretly replaced Wang He with the notoriously violent Bai Qi. When Zhao Kuo left his fortifications, Bai Qi used a Cannae maneuver, falling back in the center and surrounding the Zhao army from the sides. After being surrounded for 46 days, the starving Zhao troops surrendered in September 260 BC. It is said that Bai Qi had all the prisoners killed and that Zhao lost 400,000 men.