One assumption is that the US has intended to withdraw from Iraq from the onset. The US has an enormous number of strategic military bases scattered around the globe. It never completely withdrew from either Germany or Japan after WWII. It maintains a military presence in South Korea. As a result of the war in Afghanistan, the US acquired a number of military bases in Central Asia, not only in Afghanistan but also in several neighboring former Soviet republics. It is well known, and was easily demonstrable prior to the invasion, that the principle justification for war, namely the threat of weapons of mass destruction, was a fabricated pretext. Although chosen as the selling point for public consumption, it is self-evident that the "threat" of Iraq was simply not the true motive for the invasion. Rather, if we assume the historical norm is being followed, and if we trust documents expressing the views of policymakers within the US government, the goal of the invasion was hegemony over what has been long been regarded as a region of the utmost strategic importance, primarily due to its rich resources in oil and gas. There is little reason to believe that US has any intention whatsoever of abandoning the bases in Iraq it has acquired as a result of the invasion.
Another unquestioned premise is that US forces are a stabilizing, rather than a destabilizing, presence. The resistance to occupation began almost immediately after the invasion, and grew steadily during just the first few months of the war. Ethnic and religious tensions were an outcome of the invasion predicted well in advance, but the common image represented to us by politicians and the media of US forces acting as peacekeepers keeping Shiites and Sunnis from tearing each other apart is a dangerous delusion.
The role of the US military in Iraq is to maintain dominance of and control of important property. While the military allowed other civilian infrastructure to be looted in the breakdown of law and order that followed the invasion and was predicted beforehand, it did take steps to control and protect key locations related to the oil industry. The Green Zone in Baghdad is another important piece of property the US military is charged with maintaining control over. It represents the seat of government, which exists only because it was created by the US. This government grants an air of legitimacy to the US occupation, but would quickly collapse if weren't propped up by the US military. Most Iraqis don't want to live under foreign military occupation and want the US out. If they were to obtain for themselves a truly democratic government, that would be precisely the immediate outcome.
The US, to cite another popular axiom of the accepted framework taken as an article of faith, is trying to bring democracy to the region. The long history of US interventions abroad presents a serious challenge to this interpretation of its foreign policy. Its conduct in Iraq since the invasion does not seem to indicate a departure from a history of undermining democracy, and the theory is problematic.
We may recall the elections in Iraq resulting in a "sovereign" government that the US proudly proclaimed as a major accomplishment, evidence of the success of its invasion and overthrow of the Saddam Hussein regime. The obvious paradox of calling a government dependent upon foreign military occupation "sovereign" is almost universally disregarded, with most commentators simply pretending this contradiction does not exist (although the blindness to this dilemma is nonexistent if it so happens that a regime is supported by foreign militaries other than the US, such as was the case, to cite just one obvious example, with the Soviet occupation of Afghanistan).
With selective amnesia, we may forget that the US initially opposed those elections, preferring to postpone them until after a government consisting solely of members appointed directly by the US had adopted a constitution. Many Iraqis rose in protest and demanded elections be held earlier, so that an elected government would form the constitution, forcing the US to concede. We may set aside revisionist history claiming this as a victory for US policy: it was a clear policy failure for the US. Although the elections were marginal insofar as democratic measures are concerned (voters didn't even know who the candidates were until it was time to cast their ballots), this nonetheless represented the strong desire to bring democracy to their country in the face of overwhelming obstacles and was a major political victory for the people of Iraq.
Sectarian violence certainly plays a role in the current crisis, but if solutions are to be found, misconceptions and delusions about the role of the US in Iraq must be laid aside. A preponderance of the Iraqi violence is directed against US forces and those Iraqi forces allied with the US. Conversely, US violence is directed against those forces that oppose its presence in their country. This violence continues for one clear and simple reason: Iraqis want the US out. It easily follows that were the US to leave, the violence would be largely mitigated. Coalition generals have said as much, but policymakers are not willing to heed such advise, preferring to hear that more firepower, more violence, is the answer (comparisons to Vietnam abound, and must be taken with caution, but there are certainly some valid parallels; obvious lessons that should have been learned, but haven't, certainly apply).
The obstacle most people have with arriving at this simple conclusion is the notion that with the withdrawal of the US, the violence would increase, rather than decrease, and outright civil war (which many observers say already exists) would erupt. There is an underlying assumption that the Iraqi people are incapable of governing themselves, and hence require the US presence to maintain order. This sense of cultural superiority is a common theme among the empires of history, which have always maintained that without their stabilizing influence, the "barbarians" of their vassalages would bring about the collapse of civilization itself, at least locally, if not, due to variations of the "dominoe" theory, within the heart of the empire itself.
We may choose to begin with the alternative assumption, that Iraqis are perfectly capable of governing themselves, without US interference. Of course, this is not to say the US should negate its responsibility to the country. Indeed, there are any number of actions, or, as the case may be, inactions, an occupying power may take that are regarded as war crimes, among the "accumulated evils" that rightfully make wars of aggression "the supreme international crime", as defined at Nuremberg. The US, therefore, not only has a moral but also a legal obligation to help aright the wrongs in Iraq that have resulted, both directly and indirectly, from the invasion.
Among its responsibilities are the costs of reparations. The US vainly proclaimed prior to the invasion, in an attempt to make the war seem more palatable to American taxpayers, that the Iraqis would largely pay for the expenses of war and rebuilding. Iraqi oil, we were told, would help the war and reconstruction pay for itself. That such a declaration could have the result of soothing concerns of Americans, rather than causing outrage, perhaps says just as much about the American people as it does their government.
The notion that withdrawal will equate to abandonment of Iraq is another mental obstacle to arriving at the most obvious immediate step to end the violence and begin working towards order. The US should by no means abandon Iraq, and, as just noted, it has moral and legal obligations not to do so. Withdrawal does not imply abandonment. On the contrary, the US should commit itself to supporting Iraqi efforts to create a democratic government. This would require more than just lip service, meaningless declarations of benevolent intent, and a sustained effort, such as using its enormous influence to help bring Iraqi parties in opposition with one another to the conference table.
The prerequisite for any real solution would be the abandonment of US policies declaring a US "right" to interfere in the internal affairs of other nations to further what it perceives to be its own interests, the abandonment of ideologies regarding war as an acceptable alternative to peaceful means of settling international disputes. In short, it would require the abandonment of a foreign policy that unavoidably conflicts with democratic ideals and the principle of self-determination and so often serves to undermine them.
Although US policy is implemented with the belief that it serves America's interest, it is self-evident that the opposite is most often the case, and Iraq is hardly an exception. US interventions abroad, including the overthrow of democratic governments, have historically been disastrous for American long-term strategic interests. What is called the "war on terrorism", predicated upon the Bush Doctrine of "preemption", as well as its evolution into a doctrine of loosely-defined "prevention", which essentially states that the declaration of the existence of some alleged "threat" to US interests is justification enough for the use of violence, is not so much a radical new foreign policy as it is a continuation of policy that has existed long before the terrorist attacks of September 11, 2001, which serve as perhaps the clearest example of how, despite delusions to the contrary, US foreign policy is harmful to the interests of the American people.
There are no simple solutions to resolve the crisis in Iraq, and it would be a mistake to pretend otherwise. But if solutions are to be found, the most imperative of which is to bring an end to the violence and bloodshed, then we must cast aside myths about the US role in the world, be more willing to question dogmatic assumptions, consider a wider range of possibilities than those presented to us in the limited framework of elite consensus, and seek more honestly to assess the roots of the problems Iraq is faced with, beginning with the US role in and responsibility for the current situation.