Iraqi Shiite tribal fighters in Baghdad's Sadr City raise their weapons and chant slogans against the Islamic State after authorities urged Iraqis to help battle the insurgents on June 18. (Khalid Mohammed/AP)

When it comes time for history to be written, one of the most important turning points in Iraq's current crisis may not have been created by guns or bombs. It may have been spurred by a handwritten letter.

The Post's Loveday Morris reports that a message from Grand Ayatollah Ali Sistani was key in convincing Iraq's political elite that embattled Prime Minister Nouri al-Maliki needed to go. The letter from Sistani, sent to leaders of Maliki’s Dawa party July 9, spoke of the "need to speed up the selection of a new prime minister who has wide national acceptance." Not long after the letter was received, Haider al-Abadi, a deputy speaker for Iraq's parliament and also a member of Dawa, was called upon to lead the country. On Thursday, Maliki finally admitted defeat.

It's a bold move. While few people had doubts about Sistani's theological power, he has rarely acted so directly to influence politics. The 84-year-old Islamic cleric, infrequently seen in public and generally circumspect when making announcements, is a member of the "quietest" Shiite tradition that is suspicious of religion and politics mixing. However, Iraq's crisis may now be so bad that Sistani is taking action – and we may just be seeing the start of it.

Born to a family of religious scholars in Mashhad, Iran, Sistani only moved to his current home, the Iraqi holy city of Najaf, later in life. He was prodigious in his scholarship of the Muslim faith, and soon an important religious leader. In 1992, his religious authority was recognized when, after the death of Grand Ayatollah Imam Abul Qassim al-Khoei, he was selected to lead the most important hawza in Najaf, arguably the most important city in Shiaism.

During Hussein's dictatorship, Shiite Muslims faced suppression by the ruling Ba'ath Party, and both Sunni and Shiite clerics were forced to either keep quiet, flee the country or face serious persecution and even death. Sistani kept a low profile. After the the 2003 invasion of Iraq, however, Sistani gradually took a far more prominent role in leading Iraq's Shiite majority, surprising many outside observers.

They were tentative but important steps. In June 2003, for example, he released a fatwa that called for an elected assembly to draft a constitution. Then, in August of the next year, he helped broker a peace deal between Moqtada Sadr's Shia militia and U.S. and Iraqi forces. He urged restraint from Iraqi Shiites in the face of attacks from Sunni extremists.

For these things and more, Sistani earned plaudits for his actions from many observers: In 2005, the New York Times' Thomas Friedman suggested that he should be given the Nobel Peace Prize, for instance. You can get a sense of Friedman's argument here:

In many ways, Mr. Sistani has played the role for President George W. Bush that Nelson Mandela and Mikhail Gorbachev played for his father, President George H. W. Bush. It was Mr. Mandela's instincts and leadership — in keeping the transition to black rule in South Africa nonviolent — that helped the Bush I administration and its allies bring that process in for a soft landing. And it was Mr. Gorbachev's insistence that the dismantling of the Soviet Empire, and particularly East Germany, be nonviolent that brought the Soviet Union in for a soft landing. In international relations, as in sports, it is often better to be lucky than good. And having the luck to have history deal you a Mandela, a Gorbachev or a Sistani as your partner at a key historical juncture — as opposed to a Yasir Arafat or a Robert Mugabe — can make all the difference between U.S. policy looking brilliant and U.S. policy looking futile.

Of course, that passage looks a little foolhardy given Iraq's current situation. As Iraq collapsed into chaos in 2006-2007, Sistani again began to look like a more marginalized figure compared to more politically active leaders like Sadr (Sadr, who has less religious authority, comes from a family of important religious scholars who opposed the "quietist" school). After the United States withdrew from Iraq, Sistani rarely spoke out publicly.

The chaotic and disastrous events in Iraq over the past few months appear to have led to a shift in Sistani's thinking. Notably, there a clear break with Maliki, who had filled the government with Shiite allies and had previously enjoyed Sistani's approval. As the Sunni extremist group the Islamic State began to capture huge parts of Iraq and Maliki's government began to look less and less capable, Sistani lost patience with Iraq's prime minister and stepped in himself. In June, he called for Shiite Muslims to take up arms to fight the advancing Sunni Islamist threat (a call many answered by forming militias). Last month, he issued a thinly veiled warning to Maliki to not stay in power. July's letter now shows he was actively working against the prime minister.

Given the widespread belief that Maliki was a disastrous leader, should we dust off Sistani's Nobel Peace Prize application? Some already have. However, there is certainly more to Sistani's move against Maliki than a desire for international plaudits. In a long and fascinating profile of Sistani for the Boston Review, Mohamad Bazzi argues that the creeping Iranian influence over Iraq's political elite may have led Sistani to get more politically involved. Bazzi makes a compelling argument that a struggle, both geopolitical and theological, between Sistani and Iranian clerics may shape the future of Iran.

If nothing else, Maliki's ouster is a reminder of the power Sistani welds, should he choose to use it.  “Before this, no one in the leadership had openly expressed an opinion about a change,” Ali al-Alaq, a Dawa party parliamentarian, told The Post. “But after, we were unanimous, or actually 10 to 1.” The one member of the Dawa party’s 11-person leadership committee to disagree was apparently Maliki himself.