Legalist thought took shape across several generations of Warring States statesmen who shared a conviction that Confucian appeals to virtue and ritual could not by themselves hold a state together. Shang Yang, serving Qin from around 361 BCE, rewrote its laws so rank and reward followed measurable performance, chiefly military service and farm output, rather than birth, and made punishment uniform regardless of who committed the violation, work credited with turning Qin into the most formidable military power of its age. Shen Buhai developed shu, technique for controlling officials without needing personal virtue, and Shen Dao argued a ruler's power rests on shi, the authority of the office rather than any quality of the person holding it.
Han Feizi, of the ruling house of the state of Han, died in 233 BCE in the custody of the king of Qin, having drawn these strands into one argument. He rejected the premise that good government follows from cultivating virtuous rulers, since virtue cannot be verified at scale while clear law, consistently enforced, requires no such trust, and he was contemptuous of the followers of Confucius and Mozi alike, accusing them of misleading rulers with manipulative argument.
Qin used these methods to out organize and conquer every rival state, unifying China in 221 BCE. The rigor that built that success also made the dynasty widely hated, and it collapsed within fifteen years. No later dynasty called itself Legalist again, and the philosophy was denounced almost immediately, but the apparatus it designed, uniform law, measured performance and record keeping, was never abandoned, persisting for centuries inside governments that described their own values in Confucian terms.