President George W. Bush and British Prime Minister Tony Blair repeatedly stress that the military campaign against global terrorism is not a "war on Islam." But military planners and policymakers acknowledge that understanding Islam's internal dynamics--the ideas that unite and the controversies that divide the world's 1.2 billion Muslims -- will be critical to solidify a coalition to contain and defeat Islamic militants.
"There are core things that every Muslim believes, but beyond those things you can find an exception to virtually every generalization you hear," says Ali Reza Abootalebi, a professor at the University of Wisconsin at Eau Claire who specializes in social development in the Middle East.
No short survey can do justice to the vast diversity of modern Islam, a 1,400-year-old faith that stretches from sub-Saharan Africa to Indonesia. Muslim culture claims figures as diverse as Saudi militant Osama bin Laden and Indian-born novelist Salman Rushdie to U.S. boxing great Muhammad Ali and Libyan strongman Muammar Qaddafi. Theological disputes as old as the faith itself are compounded by ethnic divisions, historical variations and accommodations to local political realities.
Despite the identifcation of Islam with its Middle Eastern roots, less than one-quarter of all Muslims are Arabs. India, among the most vocal critics of extremist Islamic militancy, boasts the world's second-largest Muslim population, trailing only Indonesia, yet Muslims make up just 14 percent of its population. An estimated 6 million followers of Islam reside in the United States.
"Islam is by no means a monolith" says Thomas Lippman, author of Understanding Islam. "The differences in social practices, political thought, the feel of everyday life can be vast. Fly from Tripoli, Libya, to Dubai in the United Arab Emirates -- two prominent Muslim capitals -- and you get a totally different impression."
But Islamic scholars say a grasp of the basic divisions within the faith is critical to an understanding of the larger challenge facing the Muslim world and the United States in the months and years ahead. It matters, they say, that Shiite (pronounced "she-ite") Muslims are vastly outnumbered by Sunni Muslims but that Shiites are the dominant faith in Iran, Iraq, Lebanon and among some of the rebels fighting Afghanistan's ruling Taliban militia. It matters that Saudi Arabia, a longtime U.S. ally and home to Islam's two most sacred cities, Mecca and Medina, practices a strict offshoot of the Sunni faith -- Wahhabism -- that strongly influenced Osama bin Laden, suspected mastermind of the Sept. 11 attacks, and his followers in Afghanistan and Pakistan (see sidebar). It matters that Central Asian states such as Uzbekistan and Tajikistan, potentially critical allies in the military strikes against neighboring Afghanistan, are themselves moderate Islamic regimes confronting the same kind of radical Islamic elements that dominate the Taliban.
Complicating matters for a Westerner trying to understand Islam's various strains is the fact that "Islam has no Vatican," adds Lippman. While all Muslims read Islam's holy book, the Koran, "there's no one central authority Muslims can look to. There are theologians, but no sacraments and, strictly speaking, no clergy."
The most basic division in the Islamic world is between the Sunni majority and the Shia minority, a split as profound and enduring as the schisms among the Roman Catholics, Protestants and Eastern Orthodox faiths in Christianity. Sunni, or "traditionalist" Muslims make up the vast majority of the Islamic faithful, with estimates as high as 90 percent. Most Muslim nations feature a majority Sunni population and a significant Shiite minority. (In the United States, Sunnis make up more than 72 percent of the Muslim population, and Shiites account for 11 percent, with the remainder from other branches.)
Sunnis trace their faith to the tradition established by the first successors to the prophet Mohammed after his death in 632, in particular the line of caliphs beginning with his father-in-law, Abu Bakr, and ending with the prophet's son-in-law, Ali. …