What happened
Qin conquered the six remaining Warring States in turn: Han in 230 BC, Zhao in 228 BC, Wei in 225 BC, Chu in 223 BC, Yan in 222 BC, and finally Qi in 221 BC. King Zheng, now ruler of a unified China, proclaimed himself Shi Huangdi, the First Emperor.
Background
The victory followed a century of Qin strengthening after Shang Yang’s Legalist reforms in the 4th century BC, which gave the state strong armies and an efficient administration.
Consequences
Feudal states gave way to commanderies and counties, and the script, currency, and weights and measures were standardized. The imperial template Qin created lasted, through many dynasties, until 1912.