How did Qin Shi Huang unite China in 221 BCE?

Qin Shi Huang, born Ying Zheng, united China in 221 BCE by leveraging the military and bureaucratic strength of the Qin state. By the time he ascended the throne in 246 BCE, Qin was already the most powerful of the warring feudal states, utilizing a totalitarian philosophy known as Legalism to organize its government and military.12

To achieve unification, Ying Zheng relied on the counsel of his minister Li Si, employing espionage, extensive bribery, and the leadership of skilled generals to systematically eliminate the six remaining rival states. Following the annexation of the state of Qi in 221 BCE, he proclaimed himself Qin Shi Huang, the "First Sovereign Emperor".21

Once in power, he solidified this unity through radical reforms:
* Centralization: He abolished the feudal system, divided the empire into military districts, and appointed officials directly responsible to the central government.23
* Standardization: He mandated uniform weights, measures, currency, and axle lengths for carts, and simplified the Chinese writing system to ensure administrative consistency.123
* Infrastructure: He ordered the construction of a vast network of roads and canals and linked existing fortifications to create the first Great Wall.123