Attacking the Shiites' holiest shrine might do the trick.
Apparently al-Zarqawi called them "aspiring snakes” and “cunning scorpions”. In an intercepted letter he revealed this plan:
“The only solution is to attack the Apostates—the Shiites—whether their religious or military ranks or any others among them…until they become hostile towards Sunnis.” The end result will be an internecine struggle that, according to Al-Zarqawi, will force “the Americans
enter into a secondary conflict with the Apostates; that is what we need.”
http://www.worldpress.org/Mideast/1829.cfm
Incredibly this seems to be exactly what has happened.
I think the whole confrontation with al-Sadr was unnecessary and should have been avoided.
As Josh Marshall put it:
"As the shrewdest thinkers on the left and the right concede on this issue, our true strategic challenges in the Muslim Middle East are not conventional military ones, but hearts-and-minds challenges. The trick is to figure out how we can solve or ameliorate that hearts-and-minds problem while simultaneously destroying the relatively small (in numerical terms) but highly lethal groups that constitute an imminent danger. Or, to put it more crisply, how do we wipe out al Qaida (and al Qaida-like groups) without generating so much bad blood in the Islamic world that the Islamic world keeps producing new al Qaidas faster than we can destroy them?
It's not clear to me necessarily what the best way to strike that balance is. But I think this is probably the worst way -- engaging in pitched battles with fighters who pose no direct danger to the US whatsoever in a way that does profound damage to our standing within the population that al Qaida and other similarly-inclined groups hope to do their recruiting.
On Iraq specifically, think about where we've gotten ourselves. The Shi'a were supposed to be our friends. They were the ones most lorded over by Saddam. They were the community upon which we intended to build an Iraqi democracy."
http://www.talkingpointsmemo.com/archives/week_2004_08_08.php#003273