Ok kiddo, so a long time ago, there were two kingdoms called Aragon and France, and they didn’t really like each other very much. They had some arguments about who got to own some land and about who was allowed to travel through certain areas. It was kind of like when you and your friend have a fight about who gets to play with a toy.
Well, to try and stop all their fighting, they made an agreement called the Treaty of Monzón. It was like a special promise that they made to each other. In this treaty, they agreed to share the use of some places and to allow each other to travel through certain parts of their land. It was kind of like when you and your friend decided to take turns playing with the toy so you both could have a turn.
But that's not all! They also promised to help each other if an enemy tried to attack one of them. It was like when you and your friend decided to fight together if someone else tried to take your toy away.
So basically, the Treaty of Monzón was like a big truce between two kingdoms so they could stop fighting and start being friends.