Okay kiddo, so a long-long time ago, there was a big war called the Polish-Soviet War. The Poles and the Soviets were fighting over land that they both wanted.
After a lot of fighting, they finally stopped and said, "Okay, let's talk about how we can end this war and live in peace."
They had a meeting in a place called Riga, which is in Latvia. The leaders of both sides talked and agreed on certain things.
One of the big things they agreed on was that the Poles would get some of the land they were fighting for, and the Soviets would get some of it too.
This agreement was called the Peace of Riga. It was a big deal because it finally ended the war and allowed people to live in peace.
Just like when you and your friend share a toy and agree to be friends and share, the Poles and Soviets agreed to share the land and be friendly.