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 Great Wall of China
Qin was originally a state on the western fringe of the Chinese political sphere, but it grew into a formidable power in the later parts of the Warring States period when it aggressively expanded in all directions. In the north, the state of Wei and the Yiqu built walls to protect themselves from Qin aggression, but were still unable to stop Qin from eating into their territories. The Qin reformist Shang Yang forced the Wei out of their walled area west of the Yellow River in 340 , and King Huiwen of Qin (r.338–311) took 25 Yiqu forts in a northern offensive. When King Huiwen died, his widow the Queen Dowager Xuan acted as regent because the succeeding sons were deemed too young to govern. During the reign of King Zhaoxiang (r.306–251), the queen dowager apparently entered illicit relations with the Yiqu king and gave birth to two of his sons, but later tricked and killed the Yiqu king. Following that coup, the Qin army marched into Yiqu territory at the queen dowager's orders; the Qin annihilated the Yiqu remnants and thus came to possess the Ordos region. At this point the Qin built a wall around their new territories to defend against the true nomads even further north, incorporating the Wei walls. As a result, an estimated total of of Qin walls (including spurts) extended from southern Gansu to the bank of the Yellow River in the Jungar Banner, close to the border with Zhao at the time.