Of course, ethnicity is a fairly fluid thing, and could be modeled down to tribal affiliation if necessary (although it sounds like at the level you're talking about this would be a touch too micro). I'd be tempted to take it one step further and have ethnicity and "outsider" status modifiers, with "outsider" (or whatever) applying to US/Western folks (with a higher negative, at least at first) and then the internal ethnic considerations. Over time, one player could work to lessen the "outsider" penalties (although they'd likely never go away completely).