"Well, yeah, I guess so, but a lot of people come from an 'Earth' with a similar history. It's definitely the same world, but in different variations. Stuff like, uh, the Roman Empire and the French Revolution and colonizing the Americas and the World Wars... The big events are the same, but the details are different. And then there's people like Sokka and Katara and Zuko: they're all from the same world, and it's not the usual 'Earth.'"