[Why] After the death of King Wu, the young King Cheng ascended and Duke of Zhou took regency. This prompted dissatisfaction and suspicion among Guanshu, Caishu, and other royal kin stationed in former Shang lands to watch over the surviving Shang remnant. [What] Guanshu and his peers allied with Wu Geng, son of the last Shang king, and launched a rebellion aimed at toppling the Duke of Zhou's central regime. The Duke personally led an eastern expedition and after three years of hard war put down the rebellion and executed the ringleaders. [Who] Duke of Zhou withstood political rumor and displayed unflinching political will and extraordinary military talent. The ambitious Guanshu and Caishu, in their greed for power, ended in betrayal and self-destruction. [How] The pacification consolidated the newborn Zhou and erased the last possibility of a Shang restoration. It cleared the political obstacles for the large-scale rollout of enfeoffment and for the Duke's ritual codification.
Why
The historic event of Rebellion of the Three Guards represents a key developmental peak of the Huaxia dynastic system. The crucial war that consolidated the newly founded Zhou dynasty and feudalism. By establishing this moral or administrative benchmark, it continues to shape the structural and philosophical fabric of ancient Chinese statecraft.