Okay kiddo, a long time ago in ancient Greece there was something called the amphictyonic league. It was like a club or a group of cities that were friends with each other.
They made a really important temple called the Delphic temple and they shared it with each other. And every now and then they would have a big meeting where they would talk about important things like trade, war, and peace and work together to solve problems.
It was kind of like when you and your friends work together at school or on a project. The amphictyonic league stood strong for a long time and helped keep the peace in ancient Greece.