Based on my earlier thread Can Democracy Work in Iraq
Were President Bush to come over and knock on my door and say, “Mr. Garcia, you’re in charge of making democracy work in Iraq,” after thinking it over and hearing much argument (see above thread), would be “segment Iraq.” Break it down as much as possible. Decentralize the government, giving as much autonomy to local/tribal alignments as possible (stopping short of allowing them to hold militias) - basically, make them similar to the United States c. 1780.
Local populations elect local representatives, who elect an upper legislature, who is the prime force, throw in a prime minister, but leave most of the legislation at a more local “state” level.
Of course, it is always hard to draw lines in the sand and say what stops where - they tend to blend together instead of being uniform - but after some mickey-mousing, I think it could be made to work, similar to Eastern Europe (also not properly divided, still containing more than a few border disputes, but those would be lessened by the lack of militia and oversight of a national army).
This allows the current Iraqi subdivisions to each have a slice of the pie - run their own region mostly how they want to with their own local leaders. Minimize what would be controversial. The idea would be that over time, as happened in the United States, the borders would stop looking so solid and they would gell as a uniform country.
This also leads to, initially, a large number of political parties with various motivations, but over time most would die out or merge.
This seems to me to be the cleanest way and best bet to make democracy work - division, not unification. A strong, centralized government is going to be imposing a lot of will on people. It is more likely to crack under the pressure and turn into a coup.