Okay, let's talk about the Chinese Civil War, but I'll explain it like you're five.
Imagine you have two friends, let's call them A and B. A and B have different ideas about how to play a game, and they both want to be the leader. They start arguing and fighting each other over who should be in charge.
In China, there were two groups that also had different ideas about how the country should be run. The Nationalists, led by Chiang Kai-shek, wanted a democratic government that would be in charge of China. The Communists, led by Mao Zedong, wanted a government where everyone shared everything equally.
These two groups started fighting in the 1920s, but things got really intense between them in the mid-1930s. They fought a lot of battles, and each side had their own soldiers and weapons.
The Nationalists controlled the cities and had support from other countries, while the Communists were mostly in rural areas and had a lot of support from farmers.
It went on like this until the end of World War II, when Japan surrendered and China was no longer occupied by the Japanese army. Then things got really intense between the Nationalists and Communists, and the fighting got worse.
In the end, the Communists won and founded the People's Republic of China in 1949. The Nationalists fled to Taiwan, and they still have their own government there today.
So, think of it like a big argument between two groups of people who had different ideas about how to play a game. The argument got really heated, and they started fighting each other until one side won and became the leader of the country.