Okay kiddo, let me try to explain this to you in a very simple way:
A long time ago, during a time called World War II, some very bad people called Nazis were in power in Germany. They didn't like some people who lived in Germany called Poles. And so, they made some very mean and unfair laws against them, and tried to force them out of Germany. This is called expulsion, which means making someone leave a place against their will.
So, between the years 1939 and 1944, the Nazis expelled around 1.5 million Poles from their homes in Germany and sent them away to other countries. This was very hard for the Poles because they had to leave behind their homes, families, and everything they knew. It was a very sad and difficult time for them.
But there were also some brave people who tried to help the Poles during this time. They tried to smuggle them out of Germany, or give them shelter and food. They wanted to show that not everyone was like the bad Nazis, and that there was still kindness and hope in the world.
It's important to remember what happened to the Poles during World War II, so that we never forget the mistakes of the past and work towards a better and more inclusive future.