Okay kiddo, a petty kingdom is like a really small kingdom. You know how you have your own little toy kingdom in your room with your dolls and action figures? A petty kingdom is kind of like that, but with real people and land.
Sometimes, a bigger kingdom would split up into smaller ones because people would want to rule their own area. These smaller kingdoms were called petty kingdoms because they were not very big, but still important to the people who lived there.
Just like in your toy kingdom, the ruler of a petty kingdom would make important decisions for the people who lived there. They would have their own laws, traditions, and maybe even their own language!
So, a petty kingdom is basically a small kingdom ruled by a person called a petty king. It's like having your own little kingdom, but real!