(On Screen): Muqtada al-Sadr is a half-pint Shiite cleric in Iraq who is almost certainly being funded and controlled by Iran. When things got nasty in Falluja, he (or his owners) decided it was a great time to rise up in armed revolt.
The Mehdi Army wasn't big enough to actually have a chance of winning, but that wasn't the point. I think that the hope was that simultaneous uprisings among Shiites and Sunnis might cause the Americans to come down hard militarily, using indiscriminate and excessive force, angering and polarizing Iraqi Arabs and inspiring further unrest and opposition.
al-Sadr's primary power base was certain slums near Baghdad, but he soon got chased out of them. Eventually he moved his forces, and other militants who rallied to him, to the south and seized a couple of major cities there, ones considered holy by Shiites. In so doing, he (or his owners) hoped that American military response against him would be viewed as sacrilege by Shiites in Iraq and elsewhere. That would put a squeeze-play on Sistani and other Shiite clerics who had been supporting the Governing Council and cooperating with the Coalition. If they refused to change sides, they would be discredited with the broad mass of Shiites because they did not respond to desecration by opposing the desecrators. But if they did acknowledge and condemn such desecration, there'd be no half-way. They'd have to fully switch sides.
Initially there was much hand wringing about it all, and even barely suppressed triumph amongst many, as they saw what they thought (and hoped) was the long-awaited eruption of Iraqi resentment against the evil Anglo-American occupation of Iraq. After all, "everyone knows" that the invasion was illegal, and Iraqis are worse off than they were before the invasion, and that they all have been seething in hatred and resentment. "Everyone knows" that it would just take a spark to make all of Iraq go up in flames, finally (at long last) giving Americans the bloody nose and comeuppance that they so strongly deserved which fate has been so uncooperative in dishing out to them. Nemesis, so long delayed, would finally reward American hubris. Then the Americans would (at long last) meditate about why they were so hated, hang their heads in shame, and apologize to the world and promise to change. (And ratify the Kyoto Accords and the ICC treaty.)
For a while it got pretty exciting in Iraq. The rate of American casualties rose. It looked to some as if the castle of cards was about to come tumbling down.
The American response to the simultaneous uprisings didn't achieve everything many of us hoped for, "us" being supporters of the war. Falluja is still a nest of resistance. But military operations rarely achieve perfect success, and evaluation of "success' depends on your goals. It now seems that the primary objective of the American military strategy (and it was American forces who did nearly all the fighting) was to prevent the uprisings from gaining popular support and causing Iraq to boil over in revolt – exactly what al-Sadr hoped would happen. And after the militants were defeated, it was important to try to minimize the chance they'd be able to coordinate another mass uprising later.
"Killing all the militants" was not on the list, because the strategies and tactics required to do so could very easily have inspired exactly the mass uprising al-Sadr hoped for.
To prevent the uprising from spreading, the response was slow, methodical, and relatively cool. 1st Armored Division got the job of fighting against the Mehdi Army, and it refused to give al-Sadr the provocations and incidents he needed and hoped for. Even when members of the Mehdi Army used major holy sites and at least one major cemetery for military purposes (a war crime, just in passing), the Americans didn't respond by flattening them.
Thus it was that the average uncommitted Shiite saw that the Americans treated those holy sites with more respect than the Mehdi Army did.
Shiites did consider those holy sites to have been desecrated. Sistani publicly condemned the desecration, and those responsible for it: al-Sadr and his forces. There was no general Shiite uprising.
The Mehdi Army found itself surrounded, isolated, and on the losing end of a massively lopsided campaign of attrition. They tried to borrow the tactics used by the Chechens against the Russians with considerable success, but the problem was that those same tactics failed miserably against American troops.
They were on the receiving end of small raids, increasingly tight siege, and constant predation by snipers. Occasionally the Americans would drop a precision guided bomb, which infuriatingly always seemed to kill militants or take out supply dumps. The Mehdi Army suffered hundreds of casualties and in the end had nothing to show for it.
Days turned into weeks, and it became clear that they had failed. al-Sadr started looking for a way out. So did a lot of the surviving men who had rallied to his flag; the Mehdi "Army" (such as it was) began to melt away through desertion. In the end, al-Sadr's uprising ended with a whimper, not with a bang.
al-Sadr is still alive, and he's still loose in Iraq. It would certainly be nice i