I'd recommend nomads in the great plains (would do better for most tribals between the Mississippi and the Rockies, maybe even Colorado too), Manitoba/Alberta (maybe, tribal might suit them better), and, of course, the areas around Texas. I'm imagining most of the Texan culture counties would be nomadic with nomadic Texan rulers, and a large Comanche feudal state attempting to lord over them. That would make the area even more interesting than it already is, with the cultural conflict. It also strikes me that the Aggies and Longhorns could be clans with blood feuds rather than warring states, although I'm not sure if that's the best option there. Maybe the Cowboys and the Rangers could be represented somehow as well with clan politics? Texans love their football. At a stretch I could also see them in Arixo (don't know enough about the atomicist lifestyle) or the Northwest, though it should probably stay tribal. Doesn't have that steppe feel. Definitely not New England, a nomadic lifestyle just would not work there, and it doesn't really suit them culturally. If Nomads are planned south of the border, then I recommend the deserts of northern Mexico, possibly Arixo as well. Not sure where else they could reasonably fit in in there, but I am no expert on Latin America. Anyway, no matter what you guys do I'm sure it'll be excellent, just my two cents.
