my guess? Nomadic plains indian civ, with some kind of cheap, movable mini-cities instead of the big ones we are used to. its probably the Sioux, as they are well known and nomadic. of course, how that works is another story, as you'd have to figure out what happens if its conquered, how it obtains resources, how borders work, and how you actually move/build the cities... still, if this IS what the civ is, i would DEFINITELY play it. in a way i feel its kinda likely, as all the other native civs have been some degree of city builders, while a good part of native north american civs were nomatic. my one question tho is "why didn't they do this for the huns"
The problem with the Sioux is that if the Barb axeman is indeed the UU of the NA Civ, then that Axe does not strike like a Sioux weapon at all.
The axe seems to be a Tomahawk. Tomahawk is an english word adapted from the Powhatan name for the weapon: Tamahaac.
The Alphabetical rule doesn't leave much room for other civs like Cherokee and Navajo. Up to this point i think that if this is indeed the last civ, and is Native American it can only be the Sioux or the Powhatan. And that unit artwork screams "Powhatan" to the four corners, not Sioux.