So, a long time ago, there was a group of people called the Germans. They lived in a place called Germany.
Now, next to Germany, there was a country called Poland. Germany and Poland had a lot of land borders, which means they were very close to each other.
In the old days, before we had cars and planes, people used to travel by walking or riding horses. So, the Germans and Polish people would often visit each other's countries. They would trade goods like food and clothing and talk about their cultures.
However, sometimes the Germans decided they wanted to live in Poland because they liked it there. And that's how some Germans ended up living in Poland.
Now, this started causing some problems because the Polish people and the German people had different languages and cultures. So, sometimes they didn't understand each other or get along very well.
But things got worse when a man named Adolf Hitler became the leader of Germany. He didn't like Polish people and wanted to take over their land. So, he sent German soldiers to invade Poland. This was the start of World War II.
During the war, a lot of terrible things happened to the Polish people, including the Germans killing many of them and trying to force them out of their homes.
After the war ended, Poland was no longer happy with having Germans living in their country. So, they made a new law that said all the Germans had to leave Poland.
This was very difficult for the German people who had been living in Poland for many years. They had to leave their homes and go back to Germany. It was a sad and difficult time for everyone involved.