Katyn massacre

So, a long time ago in a place called Poland, there was a big war called World War II. During this war, lots of people fought and lots of people died.

Now, after the war was over, some bad things happened. You see, there were some people who were very angry with some other people, and wanted them to go away, or even be killed.

One group of people who were angry were called the Soviet Union. They were very powerful at the time, and they wanted to get rid of some people who they thought might cause trouble for them later on.

So, the Soviet Union took some soldiers and other important people from Poland and brought them to a place called Katyn. And then, they killed them.

This is what is called the Katyn Massacre. It was a very bad thing to do, and many people were very upset about it.

For a long time, nobody knew who did it, because the Soviet Union didn't want anyone to find out. But eventually, people found out the truth, and the world learned about this terrible event.