What did emperor Qin do during 221 BC?

In 221 BC, Emperor Qin Shi Huang unified China by conquering the remaining warring states, marking the end of the Warring States period. He established the Qin Dynasty and became the first emperor of a unified China. Qin implemented significant reforms, including standardizing weights, measures, and currency, and began the construction of major infrastructure projects, including roads and the early Great Wall. His reign also saw the centralization of power and the promotion of Legalist policies.