What is Islam? Is the barbarity of September 11 rooted in the preaching of Muhammad? Or are the Islamists, the Islamic fascists bent on the destruction of all who disagree with them, merely an aberration, mixing politics, religion and violence in an appeal to the lowest psychological denominators of suicide bombers?

Historians, political scientists and psychologists are all over the place in supplying answers to these questions. Since most of the suicide bombers are young men whose minds have been drowned in propaganda, doomed to permanent adolescence, it's easy to speculate that they are a maladaptive collective of perverse minds, having become twisted twigs of humanity feeding on hate.

The historical forces at play are obvious. Bernard Lewis, a leading scholar of Islamist rage, places the fault line at the failure of the Muslim world to keep up with the West in the modern world. Diminishing Muslim power is both a humiliation and in Muslim minds a reversal of divine law, driving the losers to pick through the verses of the Koran to find justification for violence against winners. The decline of Muslim fortunes began with the fall of the Ottoman Empire and reached its nadir in recent times, encouraging the likes of Osama bin Laden, educated and wealthy, to play the David to the American Goliath.

Other scholars blame Western colonialism and imperialism, along with Judeo-Christian traditions, as contributing to the violent mentality of the extremists. These aberrations, they say, cannot be found in the teachings of Muhammad. They reason that jihad initially was aimed at an inner quest for personal not political improvement, that Islamists distorted this phenomenon for their own malevolent ends, fusing politics and religion into an all-purpose aggression for the "long-suffering victims" of Western imperial expansion.

But there's another view. "The Middle East's experience is the culmination of long-existing indigenous trends, passions, and patterns of behavior, first and foremost the region's millenarian imperial tradition," writes Efraim Karsh, a British scholar, in "Islamic Imperialism," a provocative and persuasive book. "External influences, however potent, have played only a secondary role, constituting neither the primary force behind the Middle East's political development nor the main cause of its notorious volatility."

He looks directly to the words of Muhammad, who in his farewell address to his followers ordered them to fight all men until they submit with the assertion that "There is no god but Allah." It was not coincidence that Osama bin Laden echoed these words in his glee after September 11: "I was ordered to fight the people until they say there is no god but Allah and his prophet is Muhammad."

Muhammad proselytized with violence and used violence to consolidate conquest. Occupying territory was as important as converting or killing unbelievers. When the Jews of Medina resisted Muhammad in the 7th century, he beheaded the men and sold their women and children into slavery. The prophet, who claimed to derive his power and authority from Allah, was not only head of the captured states but was the single religious authority. "This allowed the prophet to cloak political ambitions with a religious aura," writes Mr. Karsh, a professor at the University of London, "and to channel Islam's energies into its instrument of aggressive expansion." The ultimate goal would be for the world either to embrace Islam or live under its domination.

This goal was realized in part with the establishment of the Ottoman Empire, which allowed certain other religions to exist but not prosper. Christians who sought domination, on the other hand, never invoked the teachings of Christ to justify violence. Early Christianity made clear the distinction between God and Caesar, spiritual and earthly power, even though such distinctions were not always honored.

"If Christendom was slower than Islam in marrying religious universalism with political imperialism," says Professor Karsh, "it was faster in shedding both notions." The imperialistic impulse, rooted in the beginning of Islam, never fully retreated and is crucial today to understanding the shedding of blood now in the name of Allah. Although Muhammad forbade violence against the community of believers, it was easy in the chaos of the Middle East to initiate violence against differing sects with their different interpretations of the Koran.

The interpretation of the Islamist mentality as rooted in Muhammad's appeal to violence, and the Islamist determination for religious domination of the world, may not tell the whole story today, but it explains why, for millions of Muslims, the image of the warrior trumps the image of a prophet of peace -- if, indeed, there ever was one.