A long time ago, a dynasty called Zhou moved its capital city because some tribes from the north were causing trouble. After that, many local leaders wanted to be kings and fought each other for 500 years! This time of fighting is called the "Warring States" period.
Finally, in 221 BC, a powerful dynasty called Qin brought all these fighting states together. Their ruler, Ying Zheng, became China's first emperor. He even changed his name to Qin Shi Huang!
Some people in China complained that things like writing, money, and measurements were all different in different places. So, the emperor said, "Let's make everything the same!" He created new systems for writing, money, and measurements. Thanks to the Qin dynasty, China became one united country. That's why we call it "China" today—it comes from the name of the Qin dynasty.
But the emperor also did some not-so-good things. He burned books he didn't like and even killed scholars who disagreed with him. He was very strict about the law, which made some people rebel against him. Two big powers, the Chu and the Han, rose up against him. After a battle, the Han dynasty won and brought China back together. The Han dynasty lasted for a really long time and became one of the most important dynasties in China. Even today, the Chinese people are often called Han Chinese, and the characters they write are called Han characters.