Al-Qaeda blew up a bridge 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 Shi’a militias.

This particular bridge was six miles east of Mahmudiyah, the first population center south of Baghdad (between fifteen and twenty miles away). The bridge carried traffic from Mahmudiyah to al-Haswah, a city fifteen 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.