Okay kiddo, have you ever tried to share a toy with a friend? Sometimes, you might need to give your friend something in return for them to let you play with the toy. That's kind of what happened with the Gadsden Purchase.
A long time ago, the United States wanted to build a railroad that went from the east coast to the west coast. But there was a problem - there were some parts of the West that belonged to Mexico!
So, the USA decided to talk to Mexico and ask if they could buy those parts of the West. After some discussion, they agreed to sell the land to the USA for $10 million! That's a lot of money, but it was worth it to the USA because they could now build their railroad without any problems.
The land that the USA bought was called the Gadsden Purchase. It was located in what is now Arizona and New Mexico. The USA was happy to have this new land, but some people were upset because they thought the price was too high.
But in the end, the Gadsden Purchase helped the USA to build their railroad and become a bigger and stronger country. And that's what the Gadsden Purchase is all about!