Is a Shiite crescent extending from Beirut to Tehran emerging in the Middle East, as Sunni Arab leaders in Egypt and Jordan have suggested? Further, should Shiite revivalism be cause for concern among the conservative Sunni monarchies in the region, much less for U.S. foreign policymakers? Some patterns are evident—a resurgent Iran, heightened Shiite-Sunni ethno-religious tensions, both within and outside Iraq, and calls from the region's Shiite minority communities for increased representation in their respective governments. Experts say this rise in Shiite self-awareness and assertiveness has fundamentally altered the region's balance of power between Shiites and Sunnis for years to come. But much of the Shiites' development will depend on the outcome of the war in Iraq.

Shiites, the second largest branch of Islam, comprise less than 20 percent of the world's Muslims. They broke off from mainstream Islam after the death of the Prophet Mohammed in AD 632 over who should be his chosen successor. Unlike Sunnis, they believe Islam's leader should be a direct descendant of the Prophet (Sunnis say leaders can be chosen by ijma, or consensus). "From about AD 680 [when the official division between the sects occurred] onward, Shiism comes to represent essentially the protest movement within the Islamic world," says Reza Aslan, a research associate at the University of Southern California's Center on Public Diplomacy, speaking at a June 5 CFR Symposium. "It is the non-state version of Islam." Theologically speaking, Shiites and Sunnis overlap in their faiths but retain important differences—for example, Shiites allow temporary marriages, pray three times a day versus the five times common among Sunnis, reject predestination, and practice ijtihad, which authorizes qualified religious leaders to interpret Islamic law.

No. Most of the Shiites in the Middle East and southern Asia are so-called "twelvers," who believe the twelfth imam, or descendant of Mohammed's son-in-law and cousin, Ali, is the only rightful ruler of the Muslim faithful (Shiism means "partisans of Ali"); Shiite clerics derive their authority as deputies in his absence. The second largest sect of Shiism is Ismailis, also known as "seveners;" they believe Ismail, the eldest son of the sixth imam, Jafar al-Sadiq (twelvers accept his youngest son Musa al-Kazim), is the infallible interpreter of Islam.

Shiites also disagree on the role of religion in political life. Some subscribe to the theocratic Iranian model and say the state should be ruled by Islamic clerics, or ayatollahs, according to sharia (Islamic law). Others are so-called quietists, or moderates—included among them is Iraq's most senior religious leader, Grand Ayatollah Ali al-Sistani—who believe clerics should provide guidance for the faithful to interpret Islamic law but should remain outside the realm of politics.

An estimated 120 million Shiites live in pockets scattered across the globe. But the bulk of them reside in the Middle East. Shiites make up strong majorities in Iran (90 percent), Bahrain (75 percent), and Iraq (close to 60 percent); Lebanon, too, is primarily Shiite. Small but potentially powerful Shiite are found throughout the Gulf States, as well as in Pakistan (17 percent), Saudi Arabia (15 percent), and India (around 2 percent). Many of the Persian-Gulf-based Shiites, particularly those in eastern Saudi Arabia and southern Iraq, inhabit lands rich in oil, which has created tension between the Shiites and their Sunni neighbors. "There's a tremendous amount of resentment," says CFR Douglas Dillon Fellow Steven Cook, who says the Saudis consider their Shiite minorities "at best as heterodox, at worst apostates."

Shiism was born as a protest group of sorts within Islam, experts say. Since AD 680, Shiites have been marginalized in Muslim societies for religious, political, and demographic reasons. In Iraq, Shiites suffered from two major crackdowns at the hands of Saddam Hussein's Sunni Baathist regime: one in the late 1970s and early 1980s, and another after the 1991 Gulf War, when a Shiite uprising was brutally put down. In Saudi Arabia, the Usuli Shiite community, based mainly in the oil-rich province of al-Hasa, is not officially recognized by the Saudi regime. Shiites—whether Arabs or not—still largely identify themselves, Aslan says, as "a persecuted yet righteous minority surrounded by a persecuting and unjust Sunni majority." In modern times, they often have been associated with Marxists and secularists, experts say.

Yes, experts say. Shiites based in Beirut, Bahrain, and in Baghdad—whose largest slum, Sadr City, is a fertile recruiting ground for Shiite militias—are predominantly poor. Some Shiite clerics, Moqtada al-Sadr among them, have played up these class tensions to mobilize supporters. Back in the Cold War era, the communist party appealed to some Shiite communities for similar reasons. There are upwardly mobile and middle-class Shiites—many of the Shiites in Saudi Arabia, Kuwait, and Iraq reside in oil-rich areas—but the vast majority of the Middle East's wealth is dominated by Sunni Arabs (In the Asian subcontinent, there tend to be more Shiites who are wealthy landowners). Experts say this income inequality has bred resentment and a sense of disenfranchisement among some Shiites.

In contrast to rebellions waged by Iraq's Shiites in 1991 and Bahrain's Shiites in 1992-1994, both of which were violently repressed, the current assertiveness of Shiites is less combative. For instance, in Saudi Arabia's municipal elections last year, Shiites were twice as likely to vote as Sunnis. Shiites in Lebanon and Bahrain are also voting in greater numbers. Further, Shiites are expanding their cross-border cultural, economic, and political ties. Large flocks of Shiites are increasingly making the pilgrimage to Najaf, a Shiite holy city in southern Iraq that has enjoyed a revival since the ouster of Saddam. CFR Adjunct Senior Fellow Vali Nasr writes in his new book, The Shia Revival, that war in Iraq will not make the Middle East more democratic but rather more Shiite.

No. In Iraq, for example, Shiites and Sunni Arabs often intermarry, particularly among the urban middle classes. Some Iraqi tribes feature both Sunni and Shiite branches. And experts say Iraqi nationalism remains important to both groups (Shiites and Sunnis fought side by side against the British after the post-World War I collapse of the Ottoman Empire, and also against Iran in the 1980-1988 war). However, some radical Sunni Arabs, so-called taqfiris, consider Shiites to be infidels and therefore fair game for targeted killings. Among this branch of radical Islam is Abu Musab al-Zarqawi's al-Qaeda in Iraq, which considered "near enemies"—Shiite collaborators with the U.S.-led government, as well as Shiite civilians—suitable targets for suicide bombs. Some experts say the death of Zarqawi may lead the sectarian bloodshed between Sunnis and Shiites in Iraq to level off.

Experts on the Arab world disagree. Some say the so-called "Shiite crescent," which presumably includes Lebanon, Syria, Iraq, and Iran, is being overblown. First, Syria is not Shiite but Alawite, a secular sect of Islam that ascribes to Arab nationalism, which puts it at odds with Shiite regional interests. Second, much will depend on the outcome in Iraq, experts say, as well as what kind of future relations Iran and Iraq have (some liken Iran's policy in Iraq to "managed chaos"). "[The Iranians] don't hope to achieve this regional hegemony by trying to instigate Islamic revolutions throughout the region to create a Shiite crescent," the International Crisis Group's Karim Sadjadpour told the Middle East Policy Council. Adds Tehran University's Kamran Taremi: "This concept [of a Shiite crescent] is a figment of the imagination of those inside and outside Iraq whose interests require them to present Iran as a threat to the Arab world."

But other experts say Shiism, at least in the Persian Gulf region, is ascendant. "[T]hat subregion of the Middle East is beginning to be polarized, not so much between revolutionary Islam and status-quo powers but along sectarian lines," CFR Senior Fellow Ray Takeyh told the Middle East Policy Council in December. Regarding U.S. foreign policy in the region, "I would suggest that we're beginning to see the emergence of a dual-pillar policy again, but the pillars are Shiite," he adds, referring to Iran and Iraq.

Iran has the ability to influence Shiite Arabs across Iraq and the Middle East, experts say. Many of Iraq's top Shiite political leaders spent years in exile in Iran—all told, around 100,000 Iraqi Shiites took refuge in Iran throughout the 1990s—and Tehran's Revolutionary Guards are heavily involved in Iraq's predominantly Shiite south. The two countries also have close religious ties. Ayatollah Sistani's popular website is based in Qom, an Iranian holy city, and Iranians increasingly view the cleric, who is of Persian descent, as their religious leader. Beyond Iraq, Tehran funds Hezbollah, an anti-Israel, Lebanon-based Shiite group that Washington brands a terrorist organization. And Iran has important commercial links with Shiite communities in Dubai, Kuwait, and Syria. But most experts say Shiite Arabs, contrary to Egyptian President Hosni Mubarak's comments in April, do not remain more loyal to Iran than the countries where they live.