So imagine you have a cookie that you love. But then, some of your friends come and take a big bite out of it without asking. You still have a little bit left, but now it's not as good as before.
That's kind of what happened to Poland in 1772. There were three big countries around Poland - Russia, Prussia, and Austria - and they all wanted parts of Poland for themselves. They didn't ask the Polish people if it was okay, they just took it. They took a big bite out of Poland and made it smaller.
The countries who took the Polish land were called the "partitioners" and they wanted the land for different reasons. Russia wanted to control more of the Baltic Sea coast, Prussia wanted to connect its two parts together, and Austria wanted more power in Eastern Europe.
This made the Polish people very unhappy, because they lost a lot of their land, and they didn't have as much power anymore. It was like they had a cookie, but then someone took a big bite out of it and gave them less of it back. It wasn't fair.