Okay, sweetie, so let's talk about Japan and Korea. A long, long time ago, Japan and Korea were separate countries and didn't really know much about each other. But then, in the 1600s, Japan started to become very powerful and wanted to control more land.
So they decided to invade Korea a few times. That means they went into Korea's land and started fighting them. It was not very nice of Japan to do this.
Then, in 1910, Japan decided to take over Korea completely. That means they made Korea become a part of Japan and Korea didn't have their own country anymore. This was a very sad and difficult time for Korean people. They were forced to speak Japanese and their culture was changed a lot by the Japanese.
After World War II, Japan was forced to give Korea back their independence. But even after that, the two countries still had some problems. There were some people in Korea who still didn't like Japan because of what had happened in the past. And sometimes Japan would do things that made Korea upset.
Today, Japan and Korea are both independent countries and have their own governments. But sometimes they still have disagreements and arguments about things that happened a long time ago. It's important for them to work towards understanding each other and being friends.