1. Unification under Qin Shi Huang (221 BCE)
In 221 BCE, Qin Shi Huang, the first emperor of China, unified the seven warring states into a centralized empire, establishing the Qin Dynasty. This unification laid the foundation for centralized governance, standardized legal codes, and uniform systems of weights and measures. To protect the northern frontier from nomadic invasions, he initiated the construction of the Great Wall, connecting existing fortifications into a continuous defense system (britannica.com).
