Mark Bowden has an interesting column about our difficulties in creating a democratic society in Iraq. He believes rather special circumstances have to be present for a nation made up of peoples from different races, cultures, religions, etc. to develop a shared sense of "nationhood."
This is sometimes called "American exceptionalism," the idea that what we have in the United States is relatively unique and not typical of nations generally. I'm not sure I agree with him, but his point of view is worth considering.