BC221, Kingdom of Qin annexed the six kingdoms to the east. The king of Qin -- Ying Zheng became the ruler of China. But he thought the meaning of the word "King" was not great enough to show his unlimited contribution and supreme power. So he changed the word "King" into "Emperor", and became the first emperor of China -- Emperor ShiHuang.

His greatest contribution is the first integration of China:
BC230 Annexed Kingdom of Han;
BC225 Annexed Kingdom of Wei;
BC222 Annexed Kingdom of Zhao & Kingdom of Yan;
BC221 Annexed Kingdom of Chu & Kingdom of Qi;
Total: 10 years. China was integrated for the first time.
The capital city was set to Xianyang.