Shiite political ambitions are on a collision course with Sunni Arab fears of being left out. If the Shiites fail to receive what they feel is their due and if the poor state of basic services is not drastically improved, there is a very real risk of a Shiite resistance emerging. That would effectively sound the death knell of the foreign military presence n Iraq. While the current insurgency may be fragmented and ad hoc, the well-organized Shiite groups -- some of which were trained by the Iranian military and have combat experience -- would make the occupation untenable. Yet an Iraq in which the Shiites have a greater say than the Sunnis will feed the latter's fears of isolation and possible persecution, undermining any motivation to cooperate with the new order.
The article is long and well-researched, and well worth reading in its entirety.