Earth is secretly an emblem of peace for the entire galaxy.

Each of those other planets that keep visiting us is a warring planet who are intrigued by our ability to coexist. If we ever successfully achieve universal peace, they will reveal themselves to us and welcome us as a fellow emblem of peace. On the other hand, if we destroy ourselves with war, they will lose faith in the idea of peace and the galaxy will fall into eternal war. We are the petri dish for the idea of peace, and the outcome of our society will be the determining factor of the fate of the galaxy.