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.
Yao Xing
When Yao Chang declared a rebellion and established Later Qin in 384, Yao Xing was at the Former Qin capital Chang'an, and he immediately fled to his father. For the next several years, as Yao Chang fought with Former Qin and Western Yan, Yao Xing was often entrusted with guarding the base of operations (initially Beidi (北地, in modern Tongchuan, Shaanxi), later Chang'an after Western Yan captured and then abandoned it), while his father engaged in campaigns. In 386, after Yao Chang declared himself emperor, he created Yao Xing crown prince. He was considered to be firm and gracious, and he spent much time studying literature despite the work necessary in maintaining home base. In 392, while Yao Chang was away on a campaign, Yao Xing, at the suggestion of the general Yao Fangcheng (姚方成), executed a number of Former Qin generals whom Yao Chang had taken captive earlier. While Yao Chang was angry on the surface, he appeared to be secretly happy that Yao Xing realized the danger that these generals posed. In 393, when the Former Qin emperor Fu Deng attacked the Later Qin vassal Dou Chong (竇衝), Yao Chang, at the suggestion of the prime minister Yin Wei (尹緯), sent Yao Xing against Fu Deng, in order to establish Yao Xing's authority over the troops. Yao Xing was able to stop Fu Deng's attack on Dou fairly easily.