Referenced here. Fascinating perspective.

"The end result is that, suddenly, the Iranians held the whip hand in Iraq, had dealt Israel a psychological blow, had repositioned themselves in the Muslim world and had generally redefined the dynamics of the region. Moreover, they had moved to the threshold of redefining the geopolitics to the Persian Gulf.

"This was by far their most important achievement.

"A New Look at the Region

"At this point, except for the United States, Iran has by far the most powerful military force in the Persian Gulf. This has nothing to do with its nuclear capability, which is still years away from realization. Its ground forces are simply more numerous and more capable than all the forces of the Arabian Peninsula combined. There is another aspect to this: The countries of the Arabian Peninsula are governed by Sunnis, but many are home to substantial Shiite populations as well. Between the Iranian
military and the possibility of unrest among Shia in the region, the situation in Saudi Arabia and the rest of the Peninsula is uneasy, to say the least. The rise of Hezbollah well might psychologically empower the generally quiescent Shia to become more assertive. This is one of the reasons that the Saudis were so angry at Hezbollah, and why they now are
so anxious over events in Iraq.

"If Iraq were to break into three regions, the southern region would be Shiite -- and the Iranians clearly believe that they could dominate southern Iraq. This not only would give them control of the Basra oil fields, but also would theoretically open the road to Kuwait and Saudi Arabia. From a strictly military point of view, and not including the Shiite insurgencies at all, Iran could move far down the western littoral of the Persian Gulf if American forces were absent. Put another way, there
would be a possibility that the Iranians could seize control of the bulk of the region's oil reserves. They could do the same thing if Iraq were to be united as an Iranian satellite, but that would be far more difficult to
achieve and would require active U.S. cooperation in withdrawing.

"We can now see why Bush cannot begin withdrawing forces. If he did that, the entire region would destabilize. The countries of the Arabian Peninsula, seeing the withdrawal, would realize that the Iranians were now the dominant power. Shia in the Gulf region might act, or they might simply wait until the Americans had withdrawn and the Iranians arrived.

"Israel, shaken to the core by its fight with Hezbollah, would have neither the force nor the inclination to act. Therefore, the United States has little choice, from Bush's perspective, but to remain in Iraq."