AL QAEDA blew up a bridge in Iraq on Sunday using a suicide truck bomb, the latest in a series of attacks against bridges in Baghdad and the "belts" of territory surrounding the capital. Such bridge bombings are best understood as part of a territorial struggle between al Qaeda and rogue Shia militias.

This particular bridge was six miles east of Mahmudiyah, the first population center south of Baghdad (between 15 and 20 miles away). The bridge carried traffic from Mahmudiyah to al Haswah, a city 15 miles farther south. The goal of any bridge attack is most likely to cut a line of communications, preventing fighters and supplies from using a road to get from one place to another.

The bridge bombed on Sunday is part of the main U.S. supply route from Baghdad to Basra (known to the military as Main Supply Route Tampa). Though the attack might have aimed at harming Coalition forces along Route Tampa, it is equally likely that al Qaeda actually aimed to harm Shia militias using this same route. In the vicinity of Mahmudiyah, Route Tampa is also a line of communications between Sunni and Shia settlements. Several important roads intersect in or near Mahmudiyah, making the town an important location in the fight between different enemies of the Iraqi government. Al Qaeda and the Shia militias are contesting this route, and U.S. forces are interdicting both of these groups.

Mahmudiyah is a predominantly Shia city, with some Sunni inhabitants, and is ringed by Sunni areas. To understand the bridge bombing, it is essential to examine the enemy groups in and around Mahmudiyah and al Haswah.

Al Qaeda in Mahmudiyah 2006

Al Qaeda dominated the city of Mahmudiyah from 2004 through 2006. The organization beheaded inhabitants there, as well as terrorizing them through other means. Until January 2007, al Qaeda also controlled the triangle of territory west and north of Mahmudiyah, between the Euphrates River and Highway 8 (the main highway running north from Mahmudiyah into Baghdad). The roads allowed al Qaeda to move fighters, supplies, and weapons from Falluja (in Anbar province) to Mahmudiyah, and from there to the southern portions of Baghdad. Al Qaeda had freedom of movement in these areas. American soldiers dubbed the area the "triangle of death," and reporters have used that old description often this spring. Al Qaeda also used its position in Mahmudiyah to attack Shia areas to the south, particularly in al Haswah (30 miles south of Baghdad) in northern Babil Province.

Coalition Forces begin Clearing the Triangle

In December 2006, Iraqi and Coalition forces re-opened the market in Mahmudiyah. In January 2007, LTG Odierno began clearing al Qaeda's transit and supply routes, which followed the Euphrates River southeast of Falluja. The 2nd Brigade Combat Team, 10th Mountain Division (the Golden Dragons), established fortified positions near Yusifiyah, conducted patrols in and along the Euphrates, interdicted safe havens from Yusifiyah to Mahmudiyah, discovered major weapons caches, and destroyed car bomb factories in the triangle. American forces killed or captured many persons linked to al Qaeda in these areas, as well as in al Haswah.

Al Qaeda contested the highway from Falluja to Yusifiyah as the United States cleared it. The group detonated vehicle bombs in Amiriyah, a town south of Falluja on the west bank of the Euphrates. Al Qaeda also responded to U.S. clearing operations by kidnapping three U.S. soldiers on a patrol near Mahmudiyah in mid-May. Al Qaeda's spectacular attacks suggest that U.S. clearing operations northwest of Mahmudiyah were hampering al Qaeda's ability to operate freely there (rather than implying that al Qaeda was growing stronger or resurgent in that area which it once controlled completely). Al Qaeda has generally responded to U.S. clearing operations (in the past and in 2007) by conducting spectacular attacks, which aim to terrorize the population or coalition, rather than by directly fighting our better armed and equipped soldiers for control of territory.

Shia Militias in Mahmudiyah in 2007 In addition to U.S. forces, al Qaeda faced another challenge in Mahmudiyah in 2007: encroachment by the Jaysh al Mahdi and other Shia militias, which apparently extended their influence from the south toward the north as al Qaeda lost control of the area. Mahmudiyah is vulnerable to militia activity because it lies along the road from Karbala and Hillah (two important Shia cities) to Baghdad.

The militias operate most actively in five major Shia cities in south-central Iraq: Kut, Hillah, Karbala, Najaf, and Diwaniyah. Kut is the hub through which people, and presumably supplies and weapons, flow from Iran into Iraq. Many of the routes from Kut run, effectively, westward or southwestward through the four other Shia cities. Militia groups, or at least their supplies, move from Kut to the other four cities.

The Shia militias apparently attempted to extend their reach beyond the four cities, into the mixed areas of northern Babil Province. In March, Shia militias evidently contested al Qaeda in the city of al Haswah, which lies at the junction of the roads north from Hillah and Karbala. Al Qaeda operatives detonated a suicide bomb at a Shia mosque in al Haswah in March. On the following day, Shia militants conducted a retaliatory bombing at an empty Sunni mosque.

Al Haswah is also connected to Kut (by way of the westward road across the Tigris at Suwayrah), and thereby to the supply route from Iran to Iraq. From al Haswah, the militias seem to have moved toward Mahmudiyah, where U.S. forces captured Iranian weapons in April.

Al Qaeda is attacking important hubs along the supply line from Iran to Iraq, in addition to the contest at al Haswah. The supply of Iranian weapons presumably follows other roads from Kut. In particular, a main road from Kut runs northwest along the Tigris to Baghdad via the towns of Aziziyah and Salman Pak. The latter has been an al Qaeda stronghold since January 2007, if not before. Al Qaeda's control of Salman Pak facilitates the organization's vehicle bomb attacks on Shia areas in eastern Baghdad. By occupying Salman Pak, al Qaeda also interdicts some of the flow of weapons from Iran to Baghdad. Al Qaeda purchased or otherwise obtained some Iranian weapons, particularly EFPs, that U.S. forces recently found in Sunni areas in southern Baghdad.

AL HASWAH HAS BEEN, therefore, a very important hub for the Shia militias as they extended their influence northward, just as Mahmoudiyah was important to al Qaeda as it extended its reach south and east. The bridge that al Qaeda destroyed on Sunday lies along the road that connects the Shia town of al Haswah with the terrain north of Mahmudiyah. By destroying the bridge, al Qaeda apparently aimed to stop the supply and northerly encroachment of Shia militias, which have increasingly threatened al Qaeda's communications from Salman Pak to Mahmoudiyah.

The recent U.S. troop increase has made it possible for Coalition and Iraqi forces to operate simultaneously all along the southern belt of Baghdad. LTG Odierno has deployed U.S. forces along the semi-circle from Yusifiyah, to Mahmudiyah, to Salman Pak (where one of the newest brigades recently began combat operations). U.S. forces are also now operating in the southern portion of Baghdad itself--in Arab Jabour and Rashid. U.S. forces have never operated aggressively in all of these areas simultaneously. As U.S. forces clear regions that al Qaeda once controlled, they take casualties from al Qaeda's fortified positions and from the Shia militia's well-placed, Iranian-supplied explosively-formed projectiles (EFPs). But their increasing effectiveness is demonstrated by the fact that al Qaeda is defending an ever-shrinking territorial position in the southern part of Baghdad and its outlying areas.

Kimberly Kagan is executive director of the Institute for the Study of War and author of The Iraq Report.

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