Juan Cole chimes in giving us his view of partitioning Iraq:
[A]side from the selfish interests of all the political actors inside and outside Iraq, as a practical policy, partitioning Iraq is too risky. It would probably not reduce ethnic infighting. It might produce more. The mini-states that emerge from a partition will have plenty of reason to fight wars with one another, as India did with Pakistan in the 1940s and has done virtually ever since. Worse, it is likely that if the Sunni Arab mini-state commits an atrocity against the Shiites, it might well bring in the Iranian Revolutionary Guards. They in turn would be targeted by Saudi and Jordanian jihadi volunteers.
A break-up of Iraq might not stop at Iraq?s borders. The Sunni Arabs could be picked up by Syria, thus greatly increasing Syria?s fighting power. Or they could become a revolutionary force in Jordan. A wholesale renegotiation of national borders may ensue, according to some thinkers. Such profound changes in such a volatile part of the world cannot be depended on to occur without bloodshed. The region is already racked by the Arab-Israeli conflict and the struggle between secular and religious politics.
To my mind, the first problem with partition, which Cole doesn’t mention at all, would be the status of highly mixed cities, and especially Baghdad. My second misgiving would be how the Turks, Saudis and Iranians would react to these news states in their backyard.