[Why] At the end of the Warring States, decades of warfare had devastated the populace and crippled production. The long-fractured geopolitical landscape had nurtured a strong popular yearning for unity, and Qin's physical strength to deliver it had matured. [What] King Zheng of Qin employed Li Si and Wei Liao, executing the "befriend the distant, attack the near" strategy to annex Han, Zhao, Wei, Chu, Yan, and Qi within ten years. He formally abolished feudalism and instituted centralized bureaucratic rule. [Who] Qin Shi Huang was the first Chinese ruler with the grand ambition of universal empire, the "first emperor of ten thousand generations." Li Si was his outstanding Legalist chancellor who designed the commandery-county template for the new empire. [How] Qin's unification ended centuries of warring-state conflict and built the first centralized bureaucratic empire in Chinese history. It left the basic standardized institutions that defined the territorial and political shape of China for the next two thousand years.
Why
The historic event of Unification of China represents a key developmental peak of the Huaxia dynastic system. Forging the grand iron-axis standard of single governance. By establishing this moral or administrative benchmark, it continues to shape the structural and philosophical fabric of ancient Chinese statecraft.