The major problem with the Kurdish north is that it is not only autonomous it is also, in many respects, independent. The Kurds have their own army, which they and the Arabs down south agree could defeat the Iraqi Army if it came to a fight. The Kurds have a foreign policy and their own envoys with neighboring countries. In particular the Kurds have managed to turn Turkey into an ally against the Iraqi government. This annoys the Arabs a great deal but the Kurds and Turks are unbeatable militarily, at least when fighting Arabs. Moreover, the politicians in charge of the Kurdish north are more energetic and decisive than their Arab counterparts running the Iraqi government.
The pro-Iran Shia government continues to support Iranian efforts to ship personnel and weapons to Syria, but Iran has apparently decided the Assad dictatorship in Syria is a lost cause. The Assad’s are part of a Shia minority that has ruled a largely Sunni Arab population since the 1960s. While Iran does not want to lose Syria as a compliant client state, it appears to have done the math and concluded that the Assads are in a death-spiral. Iraq has played this both ways, by not interfering with the largely Sunni Arab tribes of western Iraq (Anbar province) from helping their fellow Sunnis across the border. The two years of violence have sent over 60,000 Syrian Sunnis into Iraq and over a 100,000 Iraqis who had fled to Syria in the last eight years to escape the Shia death squads. Those killers have been pretty quiet for the last four years, and the rebellion in Syria made going home an even more attractive proposition.
December 13, 2012: The Iraqi and Kurdish governments agreed to move their troops out of contested areas around Mosul and Kirkuk. That would happen once local militias were organized to provide security. Both sides would have to agree that the new militias were capable of maintaining order before troops were withdrawn.