It's not known precisely how many of the world's 1.6 billion Muslims are Shiites. The Shiites are a minority, making up between 10 percent and 15 percent of the Muslim population â certainly fewer than 250 million, all told.
The Shiites are concentrated in Iran, southern Iraq and southern Lebanon. But there are significant Shiite communities in Saudi Arabia and Syria, Afghanistan, Pakistan and India as well.
Although the origins of the Sunni-Shiite split were violent, over the centuries Shiites and Sunnis lived peacefully together for long periods of time.
But that appears to be giving way to a new period of spreading conflict in the Middle East between Shiites and Sunnis.
"There is definitely an emerging struggle between Sunni and Shia to define not only the pattern of local politics, but also the relationship between the Islamic world and the West," says Daniel Brumberg of Georgetown University, author of Reinventing Khomeini: The Struggle for Reform in Iran.
That struggle is playing out now in Iraq, but it is a struggle that could spread to many Arab nations in the Middle East and to Iran, which is Persian.
One other factor about the Shiites bears mentioning. "Shiites constitute 80 percent of the native population of the oil-rich Persian Gulf region," notes Yitzhak Nakash, author of The Shi'is of Iraq.
Shiites predominate where there is oil in Iran, in Iraq and in the oil-rich areas of eastern Saudi Arabia as well.
Enlarge this image
Shiite-Sunni map
Reprinted from 'The Shia Revival' by Vali Nasr. Copyright 2006 by Vali Nasr. With permission of the publisher, W.W. Norton & Co.
The Partisans Of Ali
The original split between Sunnis and Shiites occurred soon after the death of the Prophet Muhammad, in the year 632.
"There was a dispute in the community of Muslims in present-day Saudi Arabia over the question of succession," says Augustus Norton, author of Hezbollah: A Short History. "That is to say, who is the rightful successor to the prophet?"
Most of the Prophet Muhammad's followers wanted the community of Muslims to determine who would succeed him. A smaller group thought that someone from his family should take up his mantle. They favored Ali, who was married to Muhammad's daughter, Fatimah.
"Shia believed that leadership should stay within the family of the prophet," notes Gregory Gause, professor of Middle East politics at the University of Vermont. "And thus they were the partisans of Ali, his cousin and son-in-law. Sunnis believed that leadership should fall to the person who was deemed by the elite of the community to be best able to lead the community. And it was fundamentally that political division that began the Sunni-Shia split."
The Sunnis prevailed and chose a successor to be the first caliph.
Eventually, Ali was chosen as the fourth caliph, but not before violent conflict broke out. Two of the earliest caliphs were murdered. War erupted when Ali became caliph, and he too was killed in fighting in the year 661 near the town of Kufa, now in present-day Iraq.
The violence and war split the small community of Muslims into two branches that would never reunite.
The war continued with Ali's son, Hussein, leading the Shiites. "Hussein rejected the rule of the caliph at the time," says Vali Nasr, author of The Shia Revival. "He stood up to the caliph's very large army on the battlefield. He and 72 members of his family and companions fought against a very large Arab army of the caliph. They were all massacred."
More About the SeriesChronology: A History of the Shiite-Sunni SplitFeb. 12, 2007Series Overview: The Partisans of Ali Feb. 12, 2007Profiles: Key Individuals in the Shiite-Sunni Divide Feb. 12, 2007Suggested Reading: The Shiite-Sunni ConflictFeb. 12, 2007
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