Okay kiddo, so you know how when people don't agree on things, they can sometimes fight about it? Well, that's kinda what happened in Iraq back in the year 2003. A big group of soldiers from one country (called the United States) went over to Iraq to try and make some changes there. They weren't very popular with everyone in Iraq though, and some people got very upset about it.
These people who were upset decided they were going to fight back against the soldiers from the United States, and that's what we call an insurgency. These fighters didn't have a big army like the United States soldiers did, but they knew the land really well and could hide and sneak around to try and attack the other side.
This fighting went on for a long time, with both sides trying to win. The United States soldiers wanted to stop the insurgency and make Iraq a safer place for everyone. The fighters in the insurgency wanted the United States soldiers to leave Iraq and not interfere with their country anymore.
Unfortunately, the fighting caused a lot of problems in Iraq. Many people got hurt or killed, buildings were destroyed, and things were very chaotic. But eventually, the United States soldiers started to help Iraq build up their own army so they could take care of their own country and the insurgency started to die down.
It was a really tough and complicated situation, but people learned a lot from it and hopefully, it won't happen again in the future.