The Warring States and the Legalists
As Zhou authority collapsed, seven states fought for two and a half centuries — and the pressure produced an explosion of thought as rulers hired anyone with a theory of how to win. Confucians argued for virtue, Daoists for withdrawal, Mohists for universal love and better siege engineering. The Legalists argued that human nature is selfish, so build a machine of exact laws and harsh punishments that works regardless of anyone's character. The state that adopted Legalism most ruthlessly was Qin, and Qin won.
More aspirants to elite positions are produced than there are seats; surplus elites turn to factional conflict.