Human nomad
Calabim
Malakim
(Elohim)
Sheaim
(Sheaim started out as a cult in the desert. I do not remember however, if their capital remains in a desert area or not. Ashen Veil, like Vampires, was highly secretive cult for many, many years ... only openly expressed in openly evil empires, and only then once the empire felt strong enough to reveal this truth/atrocity.)
These are all desert tribes, with, imho, equal chances of arising out of the desert. These nations should be more likely to arise from a Human nomad than a temperate nomad, and (except for (Elohim)) impossible to arise from a Winterborn tribe (except for the Calabim).
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If you want to add some more nations (like Kuriotates, which could probably arise from ANY area, ESPECIALLY winterborn imho ...) you are free to do so. But these 4 should NEVER arise from Winterborn, and be the most likely to result from Nomad/desert.
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I would say that Calabim and Elohim, of these 4, would also be quite likely to arise from temperate humans, but not Malakim or Sheaim. I mean, all 4 are desert tribes yes, but the Malakim and the Sheaim specifically start in the desert during the Age of Rebirth. Meaning ... that they never started anywhere else. Malakim and Sheaim, if being formed or discovered during the age of rebirth, would 7 out of 10 times be found in the desert. Elohim and Calabim are a bit trickier, especially the Calabim. The Calabim (or at least the 2 children of Os-Gabella: Alexis and Flauros) have a habit of abandoning civilizations and taking over new tribes of humans. Calabim could equally be any terrain type (similar, actually, to the Balseraphs and Kuriotates in that regard). That being said, during the Age of Rebirth it is documented that they are indeed leading a desert tribe during this time, therefore I think their odds of desert should be higher than what would be considered 'normal'.