King Zhaoxiang of Qin
Reigning over 55 years, he was one of the longest-serving rulers during the Eastern Zhou Dynasty. Although making numerous policy mistakes during his later years, his aggressive territorial expansions were pivotal in consolidating the state of Qin as the dominant military powerhouse in the late Warring States period. It was the strategic dominance established during his reign that paved the way to Qin's eventual successful unification of China under his great-grandson, Ying Zheng.
Yan (state)
In 222 BCE, Liaodong fell as well, and Yan was totally conquered by Qin. Yan was the third last state to fall, and with its destruction the fates of the remaining two kingdoms were sealed. In 221 BCE, Qin conquered all of China, ending the Warring States period and founding the Qin dynasty.