The Mehdi Army, "a fighting force loyal" to Moqtada al-Sadr, was estimated in 2004 to "have between 3,000 and 10,000 men, armed with rocket-propelled grenades, mortars and light weapons." According to U.S. officials, "the emergence of such independent armed groups threaten[ed] the coalition forces now occupying the country" as well as the Iraqi government that was "set to take power" on June 30, 2004. "U.S. officials have vowed to 'destroy' the Mahdi army." 
"The black-garbed Mahdi Army leading the uprising is drawn from a large and volatile pool: the slums of Baghdad. 'This is the army of the dispossessed,' said one observer, Joost Hiltermann," Ewen MacAskill wrote April 8, 2004 for the Guardian Unlimited.
"Outside the militia group, no one knows how big it is; estimates vary from 3,000 to 10,000. But it has been growing fast. They are the poorest of the poor, the Shia who feel that, a year after the fall of Saddam Hussein, there is little for them in the settlement agreed between the US and the provisional government. 'It's a class thing, not just an ethnic and religious divide,' said Mr Hiltermann, director of the International Crisis Group, a think tank based in Amman which has been studying the militias," MacAskill wrote. "The Mahdi Army was born in the war's aftermath. With no one in charge, Shia clerics organised food and essentials from the mosques of Sadr City, the slum in Baghdad that is home to two million Shia.
"Security was just as important, and the clerics sent out gunmen to protect Sadr City. One of the most popular clerics was Moqtada al-Sadr—young, radical, and anti-American, whose father had been killed in 1999 by Saddam," MacAskill wrote.
In June 2003, Sadr "brought these irregulars together as the Mahdi Army. Mahdi is Arabic for 'the promised one' or 'divinely guided one', and for Shias, much more so than for Sunnis, is a figure equivalent to Christ's return on Judgment Day. One Islamic tradition speaks of fighters arriving from the east bearing black flags to slaughter unbe lievers, when the Mahdi would appear. Various figures down the centuries claimed to be the Mahdi, the one familiar in Britain being the Sudanese leader who killed General Gordon. ... The Mahdi Army is less well organised than other militias, such as the Kurdish peshmerga and the Shia Badr organisation, but most of its members have had military training in the old Iraqi army," MacAskill wrote.
- Ewen MacAskill, "Army of the dispossessed rallies to Mahdi" Guardian Unlimited (UK), April 8, 2004.
- Valentinas Mite, "From peace to war," Asia Times, April 10, 2004.
- "Who Is Moqtada Sadr?" Washington Post, August 16, 2004.
- Phillip Robertson, "City of vengeance," Salon, July 12, 2006: "A savage outbreak of retaliatory killings has pushed Iraq to the brink of civil war. In the first of three exclusive reports, our correspondent investigates the Mahdi Army's Baghdad death squads." Subscription or free preview required.