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.