Sounds like a very good idea to me. It would explain the mostly low native Dwili population (except in the Lurian lands and perhaps in the North, but those can go as the Aztecs and Incas), and we can use an American parallel without having to use actual American cultures or ethnicities.
Ethnically I was thinking about the native peoples of the north Toprak as Scandinavian, Germanic and Slavic parallels, with Turkic/Mongol/Asian enclaves in the Dongeselands and Flow Peninsula, Mediterranean peoples around the Lurias and North African/Middle Eastern peoples in southern Forland, Madina and perhaps even Aurvandil. The Sallowsite Cape would go with Persian peoples.
