In 22 1 year BC, Ying Zheng, king of Qin, successfully wiped out six vassal states in the Warring States period, and realized the first unified centralized state in the history of China. This incident was vividly described as the sweep of Liuhe by the king of Qin, which implied the feat of Qin Shihuang's unification of the world. Qin Shihuang unified the six countries through a series of war and political means and established a centralized ruling system.