I think one the first major things that'll happen after the Coalition withdrawal will be the abandonment of the revenue sharing from the oil sector. Its only pressure from the US thats compelled the Shiites and Kurds to agree to it, once that pressure is gone, it'll be finished. The civil war is going to be about the three factions trying to secure as much of the former Iraqs oil assets for themselves as possible. True, the Sunnis and Shiites each have their own wealthy backers, who will funnel huge amounts of arms and money to them, but I think the Kurds are in the best shape of all three factions, in just about every way. The biggest problem the Kurds face wont be the other two factions, it'll be Turkey. Contrary to popular opinion, Turkey would never invade. Assuming they managed to conquer the Kurdish region, what would they do with it aftewards? Keep it? Not very likely. Set up another independent Kurdish state? Then why bother invading in the first place? No, what they'll do is infiltrate (assuming they havent already) the Kurdish area with thier version of special ops forces and commit as much sabotage as possible against Kurdish infrastructure as possible, in order to weaken the government. The best outcome for the Turks would be the annexing of the Kurdish territory by either the Sunnis or the Shiites, so they'll do whatever they can covertly to bring that about.