A common objection to any kind of U.S. withdrawal from Iraq is that it's a gift to Iran. Iran is actively meddling in Iraq's politics as we speak. Should U.S. forces go over the horizon, the prospect of a powerful Iran and a subordinate Iraq stokes fears of a Shiite superstate in the region.

Is this how things will actually play out? Consider what is heppening now in Basra. The Christian Science Monitor's Sam Dagher reports on how Iraq's second-largest city is doing in the wake of the British exit from the city earlier this month. To get a sense of how fractious the place is, here's Dagher's guide to the key players in the region:

Sadrists and Mahdi Army: The movement of radical cleric Moqtada al-Sadr is a formidable force in Basra. The Mahdi Army is estimated to number 17,000 in the province. Security officials say that some of the Basra militia are infiltrated by Iran and beholden to Tehran. It opposes a super-Shiite region, but supports the ouster of the Fadhila governor.

The Council: The Supreme Islamic Iraqi Council, previously known by its acronym SCIRI, embraces four other affiliate parties in Basra:

The Badr Organization – Once the council’s Iranian-trained paramilitary arm, known as the Badr Brigade.

The Shaheed Al-Mihrab Organization – A nationwide movement headed by Ammar al-Hakim, the son of the Council’s chief.

The Sayed Al-Shuhada Movement (Master of Martyrs Movement).

The Hizbullah Movement in Iraq (no relation to Lebanese Hizbullah) and another small Iraqi party called Hizbullah al-Iraq (see below).

All five parties were previously based in Iran and have strong ties to Tehran. The Council and its affiliates hold 21 of the 40 seats in the provincial council. Badr still controls several police units, including customs.

The Pentacle House: The Council and its four party affiliates make up the Bayet al-Khumasi, or the Pentacle House. The goal: to create a nine-province Shiite group called the “South of Baghdad region.” Billboards in Basra tout the project as a “Shiite Renaissance.”

The Islamic Fadhila (Virtue) Party: Fadhila is a national party founded by Basra natives. Its spiritual leader is Najaf-based cleric Ayatollah Muhammad al-Yacoubi, who broke ranks with Moqtada al-Sadr in 2003.

The movement continues to espouse Sadrist ideas but has increasingly fashioned itself as a Shiite Arab Islamist party opposed to Iranian meddling in Iraq. It opposes the pro-Iranian Council and its affiliates over a number of issues, including the supersouthern region.

Fadhila holds 12 seats in the Basra provincial council, including the governorship and one of the two deputy governor slots in Basra. Fadhila dominates the 15,000-strong oil protection force.

Thaar Allah (God’s Revenge) Party: A small party based in Basra and headed by Yousif al-Mussawi. He is suspected by many city residents of being an Iranian agent. The party derives much of its funding from wealthy merchants who rely on it for protection. It has allied itself with the Council and its Pentacle House in the fight to oust the Fadhila governor. Mr. Mussawi blames the governor for the death of three members of his family during a raid on his party headquarters in 2006.

Hizbullah al-Iraq: A small party headed by tribal chief Abdul-Karim al-Mahamadawi, based in neighboring Maysan Province. The Prince of the Marshes, as Mr. Mahamadawi is known, has a large, armed tribal following and presence in Basra. He has tense relations with the Council and its affiliates.

Mahmoud al-Hassani al-Sarkhi: The cleric broke ranks with the Sadrists and is believed to be in the holy city of Karbala with the bulk of his militia. But he still has a following in Basra. His posters adorn many streets. The controversial cleric has challenged the authority of the marjiya, the Shiite religious authority dominated by the Najaf-based Grand Ayatollah Ali al-Sistani.

2) Iran does not appear to be playing a unifying role. The Monitor story suggests that this is because it lacks the capacity to do so:

Although Iran is closest to the council and its affiliate parties like Badr and Sayed al-Shuhada, it's also backing many other Shiite groups in southern Iraq including those that are openly using violence to oppose British and coalition troops, according to Ali Ansari, an Iran specialist at London's Chatham House.

"The Iranians are backing as many horses as they can," he says. "But there is a limit to their influence, given how fractious Shiites are in Iraq."

The Basra story is still developing, of course. Still, one wonders whether Tehran will be any more adept at nation-building in Iraq than the United States.