Reading between the lines of this brief but very good primer on the history and problems of Iraq, one gets the impression that a major impediment to any kind of functional government in Baghdad is Islam. What is needed between Sunni and Shia is trust and forgiveness and Islam is not a religion notable for its emphasis on either.
Indeed, a religion that emphasizes retribution and vengeance and which is deeply ingrained into the cultural assumptions by which people live is not likely to result in harmony between groups which have been at each other's throats for centuries. It's interesting to note that every Arab state is either a dictatorship or a monarchy. True democracy is not part of the heritage handed down to Arabs by their Islamic tutors and ancestors.
The challenge the United States faces is trying to impose a form of government based on Christian assumptions of freedom, equality, civil rights, and honesty on people who despise Christianity. Yet what realistic alternative do we have at this point but to do our best to try?
RLC