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.
King Zhaoxiang of Qin
In 273 BC, Wei and Zhao allied together to attack Han's Huayang (華陽). Qin offered military help to Han, defeating and killing 130,000 Wei soldiers, and drowning 20,000 Zhao soldiers in the Yellow River. In 269 BC, King Huiwen of Zhao backflipped on his previous promise to send hostages and concede land. In response, Qin attacked Zhao and laid siege to Yuyu (閼與). The siege was lifted after the Zhao general Zhao She (趙奢) ambushed and decisively defeated the invading Qin army. In 265 BC, Qin struck back at Zhao and captured three cities, and King Huiwen of Zhao resorted to sending his son to the state of Qi in exchange for Qi assistance, which forced the Qin army to withdraw.