First of all, I was assuming that each religious/ethnic group would more or less be a monolithic block.
I know, and acknowledged that point if you ready me again

I didn't come out and say it, because I thought it could be assumed, but the basic fact is you either have to break those political "blocks" (somehow) or just go ahead and break them up into separate states (probably not a good idea). As things stand, democracy in the US form just wouldn't work there, even if you did convince them to stop using naked force as the tool of choice (see next line).
As for reforming their culture, is that not an inherently arrogant statement?
No. Its simply something thats absolutely 100% necessary. You can rephrase it, if you want, to say change their mindset or their way of life or their political process or anything else you want. But you have to get them to stop viewing naked force as the instrument of choice -- as the first tool, rather than last -- for political disagreements. The rest of their culture is their own,
again as I acknowledged (though perhaps not is as many words), to change or not as they would.
I think you need to learn to read me more closely. One of your comments was a clear mis-reading (or missed reading) of a part of a post, the other other missed a key implied argument (which may have been my fault, I will admit...). To quote myself:
Teach them the basics of separation of church and state, freedom of speech, rule of law, and the like... but not mom's apple pie, thats all ours

. On a more practical level, I mean help them establish not just the forms but the reality of a free, democratic government, but don't try to overwrite their culture.
Each of the things I mentioned is vitally important in any democratic government. If you don't have the separation of church and state, the freedom of speech, and a genuine rule of law, any democracy formed won't be stable.
Please note that separation of church and state can be absolute, as in America, or partial (most other places) wherein while there may be an acknowledged state church, but it doesn't really matter if you're a member or not.