The alienation of Muslim immigrants in the West. Three out of four of the 9/11 pilots and two key 9/11 planners, KSM and Ramzi bin al-Shibh, became more militant while they were living in the West. It seems that some combination of discrimination, alienation and homesickness turned them all in a more radical direction. And this is true for other anti-Western terrorists. Los Angeles Times researcher Swati Pandey and myself examined the biographies of 79 terrorists responsible for five of the worst anti-Western terrorist attacks in recent memory: the World Trade Center bombing in 1993, the Africa Embassies bombings in 1998, the September 11 attacks, the Bali nightclub bombings in 2002 and last year's London bombings. We found that one in four of the terrorists involved had attended colleges in the West. Similarly, researchers such as Dr. Marc Sageman argue that many terrorists affiliated with Al-Qaeda are either immigrants to the West or second generation Muslims who have not been integrated into their European host countries. For demographic reasons (the native populations of most Western countries are in decline) and for economic reasons (the economies of many Muslim countries are in freefall), there will be an exponentially growing number of Muslim immigrants to the West in the coming years, some of whom will become alienated and adopt Bin Laden's world view.

9/11 does have something to do with a particular reading of Islamic texts. In all the many discussions of the "root causes" of Islamist terrorism, Islam is rarely, if ever, mentioned. This is surprising because if you asked Bin Laden what his war was about, he would answer that it's all about the defense of Islam. This is not to say that Islam is in any way a "bad" or "evil" religion, but on the principle that we should listen to what our enemies are saying, Bin Laden justifies his war based on a corpus of Muslim beliefs and can find enough ammunition in the Quran to give his war a patina of religious legitimacy. For instance, Bin Laden often invokes the "Sword" verses of the Quran, which urge unprovoked (pre-emptive!) attacks on infidels. Of course, that is a selective reading of the Quran as there are other verses that justify only "defensive" jihads, but the point is the Sword verses are in the Quran and therefore are the Word of God. This is not something that apologists can simply wish away. This conviction that they are doing God's will frees Islamist terrorists to conduct mass-casualty attacks of the kind that secular terrorist groups historically never undertook.

9/11 was the collateral damage of a clash within Islam. The view that 9/11 was the result of a conflict within the Muslim world was first brilliantly articulated in November 2001 in Foreign Affairs by Michael Scott Doran. Doran explained that Bin Laden's followers "consider themselves an island of true believers surrounded by a sea of iniquity and think that the future of religion itself, and therefore the world depends on them and their battle." The Egyptians in Al-Qaeda in particular, such as Ayman al-Zawahiri, hold this view, having imbibed it from the works of the jihadist theoretician Sayyid Qutb, who explained that most of the modern Middle East is living in a state of pagan ignorance. This insight animated the Egyptian jihadist belief that they should overthrow the "near enemy" regimes of the Middle East run by "apostate" rulers. It was then the next intellectual step for Bin Laden to urge Zawahiri that the root of the problem was not the "near enemy" but the "far enemy", the United States, which propped up the status quo in the Middle East and was therefore ultimately responsible for the regimes in the region. This analysis is now widely held among militants across the Muslim world.

Authoritarian regimes in the Middle East helped to incubate the militants. It was their experience in the hellish jails of Cairo, for instance, that radicalized both Qutb and Zawahiri. And it is also not an accident that so many key members of Al-Qaeda have been Egyptians and Saudis. However, with the present price of oil it is very unlikely that the Saudi regime will do much to reform politically. Meanwhile, Mubarak's government in Egypt--having made some pretense of reform with the presidential elections in September 2005 and parliamentary elections two months later--is now even more repressive than before 9/11, cracking down on judges, for instance, and imprisoning its political opponents on trumped up charges. The "Arab spring" that was touted by some commentators in 2005 now seems a distant mirage.

There can be no unified-field theory that explains what happened on 9/11; rather it was the confluence of the factors outlined above that help us understand the underlying causes of the attacks on New York and Washington. On 9/11, we were collateral damage in a civil war within the world of political Islam. On the one side there are those like Bin Laden who want to install Taliban-style theocracies from Indonesia to Morocco. On the other side, there is a silent majority of Muslims who are prepared to deal with the West, who do not see the Taliban as a workable model for modern Islamic states, and who reject violence. Bin Laden adopted a war against "the far enemy" in order to hasten the demise of the "near enemy" regimes in the Middle East, so his vision of political Islam could be installed around the Muslim world. And he used 9/11 to advance that cause. That effort has largely failed, but the underlying problems in the Muslim world remain virtually unchanged five years later and will likely provide the fuel for future attacks against us.