This is from Juan Cole. There is a lot of interesting background on the religious aspects of the conflict in Iraq. This background is really helpful in understanding how serious these attacks are as destabilizing actions.
Everyday Apocalypse in Iraq
War of the Mosques
142 Dead on Tuesday
142 persons were killed or found dead on Tuesday, and Wednesday morning two Sunni mosques in towns south of Baghdad were blown up.
On Tuesday, a huge truck bomb in Baghdad blew up a Shiite mosque dedicated to an important religious figure and killed 87 persons, wounding 214. This site was dedicated to Muhammad bin Uthman bin Sa`id al-`Amri, the second of at least four Deputies (wakil) who Shiites believe acted as intermediaries between the Hidden Twelfth Imam and believers during his first or "minor" Disappearance. Shiites believe that the Prophet Muhammad should have been succeeded by his close family and descendants. The 12th Imam, a direct descendant of the Prophet Muhammad, they say, went into hiding as a small child in 874 AD after the death of his father, Hasan al-Askari, who had been put under house arrest by the Abbasid Caliphate. During the "minor disappearance" the Twelfth Imam was said to send letters to the Shiite community, and for many years sent them, they say, through Muhammad b. Uthman.
Many Iraqi Shiites, poor, bewildered, under siege by multiple political and military forces, have become millenarians and believe that the hidden Twelfth Imam will now come back any day as the Mahdi, the apocalyptic Guided One, who will restore the world to justice in preparation for the Judgment Day.
The Sunni Arab guerrillas know that this millenarian hope and fervor sustains many Shiites and that they are touchy about it. That is why they have twice bombed the shrine at Samarra, dedicated to the father and grandfather of the Imam Mahdi, and now have hit in such a powerful and gruesome way the mosque-shrine of the Imam Mahdi's second Deputy. (A traditionalist account of the Deputies of the Imam can be found here).
Hope for the coming of the promised one is all most Shiites have left, and the desecration of sacred sites associated with the Mahdi (analogous to the return of Christ for Christians) is especially likely to set off reprisal attacks against Sunnis. Since the guerrilla strategy in Iraq is to provoke a Sunni-Shiite civil war as a way of making the country ungovernable and forcing the Americans out, attacks on symbols of the Twelfth Imam are especially effective.
One unfortunate side effect of this shrine-destruction strategy is that the shrines are revered in Iran, as well, and President Mahmud Ahmadinejad is a millenarian especially devoted to the cult of the Twelfth Imam. Sentiments of the Iranian public are also being stirred by these attacks (not to mention Hizbullah in Lebanon, and Shiites in Pakistan, Bahrain, Saudi Arabia and elsewhere, who increasingly blame the US for the desecrations). Religious politics is politics, and the US is being wrongfooted in a major way here.
The signs of the coming of the Twelfth Imam in Shiite tradition are as follows:
'The Sign consists of the following traits: the people will neglect prayer, squander the divinity which is conferred on them, legalize untruths, practice usury, accept bribes, construct huge edifices, sell religion to win this lower world, employ idiots, consult with women, break family ties, obey passion and consider insignificant the letting of blood. Magnanimity will be considered as weakness and injustice as glory, princesses will be debauched and ministers will be oppressors, intellectuals will be traitors and the reader of the Koran vicious. False witness will be brought openly and immorality proclaimed in loud voices. A word of promise will be slander, sin and exaggeration. The sacred Books will be ornate, the mosques disguised, the minarets extended. Criminals will be praised, the lines of combat narrowed, hearts in disaccord and pacts broken. Women, greedy for the riches of this lower world, will involve themselves in the business of their husbands; the vicious voices of the man will be loud and will be listened to. The most ignoble of the people will become leaders, the debauched will be believed for fear of the Evil they will cause, the liar will be considered as truthful and the traitor as trustworthy. They will resort to singers and musical instruments...and women will horse ride, they will resemble men and the men will resemble women. The people will prefer the activities of this lower-world to those of the Higher-World and will cover with lambskin the hearts of wolves."
Muqtada al-Sadr has alleged that the entire point of the US invasion and occupation of Iraq was to keep this decadent situation in place and to forestall the coming of the Mahdi by planting military bases around Iraq and the Persian Gulf. He says that the US Pentagon has an enormous file on the Mahdi.
In orther words, the US and militant Sunni Arabs are felt by many Iraqi Shiites to be playing the role of Dajjal or "Anti-Christ", a figure whose purpose is to forestall the coming of the Imam Mahdi. Shiite tradition holds that the Mahdi will come together with the Return of Christ, and that the returned Christ will kill the Dajjal. (Ironically, some of the US troops fighting the Shiite millenarians may be evangelicals who also believe that the Return of Christ is near; Iraq is a wonderland for apocalytpicism).
Ideologically, the shrine bombings of the past week and a half are far more important than any mere military maneuvers. If the US cannot arrange for the shrine of the Imam Mahdi's Deputy in Baghdad itself to be protected better than that, it will never succeed in Iraq's religious politics, no matter how many ink spots it creates.
The US offensive in Baquba, the capital of Diyala province northeast of Baghdad, is intended to root out Salafi Jihadi forces among the Sunnis that have come to dominate entire neighborhoods and entire towns in the province, which lies between Baghdad and Iran. But most of the forces involved seem to be American and Shiite (the 2,000 'paramilitary police' mentioned are surely from the Badr Corps paramilitary of the Supreme Islamic Iraqi Council [SIIC], the leading Shiite party with links to Iran). Diyala has a Sunni majority, and a lot of the problems in that province began politically in the first place because SIIC has dominated it politically. In the short term, this operation may 'pacify' Baquba. But likely it will inflict tremendous damage on the city, will cause a lot of the 300,000 or so inhabitants to flee and become refugees, and will likely not change the political situation, which is Shiite dominance of Sunnis along with some Kurdish separatist plans for parts of the province. Falluja had 2/3s of its buildings destroyed and tens of thousands of its former inhabitants are living in tent cities in the desert with bad water, and Falluja is still not secure--kidnappings, shootings, mortar attacks, even car bombings are all still taking place there and in its environs.
There is also heavy fighting between Mahdi Army forces and Iraqi government troops in Nasiriya in the south, with British troops allegedly giving some support to the government side. Typically the 'Iraqi government' forces are actually drawn from the Badr Corps and so this is in a way two Shiite militias fighting one another. These clashes have reinforced the determination of the Sadr Movement MPs to suspend their participation in the parliament, which probably therefore lacks a quorum for the rest of the summer. The Sadrists say an agreement has been reached with the governor of Nasiriyah to end the fighing.