Okay kiddo, so back in the early 1800s, the United States was a pretty new country and it was having some problems with some of its neighbors, especially a country called Britain. Britain was really powerful and had a big navy, which means it had a lot of ships that could sail on the ocean and fight other countries.
The United States didn't like a lot of things that Britain was doing. One thing was that Britain was stopping American ships and searching them to see if they had any goods from France, which was another big country that Britain was fighting with. That really annoyed the Americans because it was hurting their trade (that means buying and selling things with other countries) and it made them feel like they weren't being respected as a country.
Another thing that upset the Americans was that Britain was helping some Native American tribes fight against the United States. The Americans were trying to take more land and control more of North America, but the Native Americans were already living there and didn't want to give up their land. So, they asked Britain for help, and Britain gave them weapons and supplies to keep fighting against the Americans.
All of these issues made the United States really angry and they decided to declare war on Britain. This war is called the War of 1812 because it started in 1812. It was fought on land and sea, but it was mainly fought in North America, around the Great Lakes and the U.S.-Canada border.
The war lasted for a few years and both sides won some battles and lost others. In the end, there wasn't really a clear winner, but the United States was able to show that it was a strong country that could stand up to Britain. And even though the war was over, it helped to build a stronger sense of pride and unity among Americans.