When did China become a unified state and who was its first ruler?

A unified state appeared quite late in China. This happened in the 3rd century BC, from 220 to 210 BC, although the struggle for unification went on from about 240 BC, it was led by Qin Shi Huang.

He was able by 220 BC. capture small states on the territory of modern central China, proclaimed the Qin Empire. His empire occupied just under half of modern China, excluding Manchuria, Inner Mongolia, Uyguria, and Tibet.

During his reign, such innovations appeared:

The Great Wall of China, it was built to protect against the raids of nomads from the north.
Epan Palace and the Terracotta Army in his tomb.
Lingqui Channel.