...Basra teaches that as soon as the military surge ends and coalition forces diminish, competition between rival factions itself will surge....
The Jamestown Foundation's Terrorism Focus, 6 Jul 07:

The Militia Politics of Basra
Basra, the second largest and the richest city in Iraq, is at the brink of a major economic and political meltdown. Unless Baghdad succeeds in reaching a compromise over the country's governmental apparatus (especially over the issue of federalism), the southern city may become the greatest threat to the future of post-Baathist Iraq. Such a threat lies mainly in a struggle for power between Shiite militias and tribal forces who compete for control over oil resources, territorial domination and public capital (hospitals and schools), which are all leading to an erosion of security in a city that is the source of Iraq's economic life. Although much of this turmoil is a reflection of the unstable nature of the transitional process, the current situation in Basra may represent a future scenario for Iraq that is made up of political factionalism and devoid of a functional government.

At the center of Basra's meltdown lies the ongoing conflict between different Shiite factions, mainly vying for control over Basra's energy industry and oil smuggling. Domination over local governance through confrontation, and at times violence, has become the routine method of conducting politics in a city that appears to be breaking apart into territories governed by different militias. Such political conflict, however, also includes competing visions of post-Baathist Iraq, as each Shiite militia advocates a particular ideological agenda (regionalist, nationalist and sectarian), while seeking popular support from various segments of the Shiite community in Basra and other southern cities.....