Okay kiddo, so you know how sometimes different countries work together to try and solve big problems, like how mom and dad might team up to make dinner? Well, that's kind of like what happened in Afghanistan.
Since 2001, a whole bunch of countries (like the United States, the United Kingdom, and Canada, among others) have been working together as a group called the Coalition to try and help the people in Afghanistan be safe and happy. They wanted to make sure that bad people who hurt others didn't get to do that anymore, and that everyone could live in peace.
But sometimes, when people are trying to make a difference in a tough situation like this, bad things can happen. There were times when members of the Coalition got hurt or killed while they were trying to help out in Afghanistan. That's what we mean by "coalition casualties."
It's really sad and scary when that happens, and we want to do everything we can to make sure that everyone who is working to make a difference is as safe as possible. The people in the Coalition know that it's a tough job, but they believe that it's really important to keep trying to help out wherever they can.