I already shared my vision of Athas history here:
However, as a resume:
- Nature-masters brought people from other planets to repopulate Athas. That’s why races and civilizations are the same as in other settings. They spread and populate vast regions of Athas.
- Zik-Chil are mutated nature-benders, which also made the thri-kreen intelligent to be used as a weapon.
- Rajaat was a nature bender/Zik-Chil creation. He shared the same vision that bringing other races to Athas was an abomination. That’s why he started the cleansing wars.
- The surviving civilizations moved back to the Tyr Region, as the ultimate habitable place.
-North is the Ecuator and it’s too hot to live.
-South, you have the Dead Lands. What’s beyond that? Maybe some civilization still exists in the South Pole
-West, the Kreen Empire, still hating other races due to their genetic-memory.
-East, was blocked by the Dragon and Ur-Draxa until very recently. Now, some old lands and some old city-states will start to enter into play. - All the history from the end of the Blue Age to today, took more or less 1500 years.