Even after six years on the ground, problems are beginning to build as American forces in Iraq move toward withdrawal over the next few years.
The question of who is going to rule after the Americans leave is up in the air and will not be resolved until U.S. forces have gone. Apart from the division of political power, there does not exist, for example, a law to govern oil revenue sharing. In the meantime, the American presence will be used by various Iraqi elements to try to improve their positions in advance of the withdrawal.
Since the resolution of the question will almost certainly be by force, preliminary maneuvering will also almost certainly involve force. At this point there is skirmishing, and the familiar weapons of car bombs and assassinations are appearing with greater frequency.