So, imagine if you played a game with your friends and you divided into two teams: Team A and Team B. Team A wins the game, and they are really happy and proud of themselves. But when they want to celebrate their victory by doing something special, Team B says "No, we don't want to celebrate with you, we don't like you". Team A feels sad because they thought Team B were their friends, but now they don't want to be around Team A.
That's kind of what happened in a place called Mostar a long time ago. There were two groups of people who lived there, and they didn't like each other. One group was called the Bosniaks and the other group was called the Croats. They had a big fight, and many people from both groups died.
After the fight, they wanted to remember their loved ones who had died. But they couldn't agree to remember them all together, because they still didn't like each other. So they built two different places to remember their dead people. One place is for the Bosniaks and one place is for the Croats.
This is called a partisan memorial cemetery. It's a special place that remembers people who fought for a certain cause, or who were from a certain group of people. It's like a reminder to everyone who goes there about what happened in the past, and to never forget the people who lost their lives in the fight.
So in Mostar, there are two partisan memorial cemeteries, one for the Bosniaks and one for the Croats. Even though they are separate places, they serve the same purpose: to remember the people who lost their lives.