AFTER 9/11 BROUGHT RADICAL ISLAM to the country's attention, some Americans wondered, "Why do they hate us?" Since then, many answers have been offered. But the best way to understand what drives jihadists is an examination of their own words. To that end, Professor Mary Habeck's book Knowing the Enemy: Jihadist Ideology and the War on Terror (Yale University Press 2006) makes a vital contribution. It is the most thorough and valuable explanation of jihadist ideology available in English to date.

Central to Habeck's argument is the failure of most Western scholarship to comprehend religion as a sociopolitical factor. Most academics, journalists and policymakers in the increasingly secular West have never considered religion an important part of their lives, and have trouble understanding how it can be a prime motivating force in world affairs. Thus, they tend to look to factors such as poverty, colonization, and imperialism to explain jihadist grievances.

Such an analysis fails to provide us with deep insight into jihadist thought. As Habeck points out, U.S. support for Israel alone doesn't explain the 9/11 attacks. Jihadist ideologue Sayyid Qutb's anger was focused on the United States in the early 1950s, more than a decade before America became associated with Israel. Nor do colonialism and imperialism provide a convincing answer. Muhammad ibn Abdul Wahhab "developed his version of radical and violent Islam long before the West colonized Islamic lands, indeed at a time when Islam seemed triumphant."

SO WHAT DOES EXPLAIN jihadist hatred of the West? It is true

While Habeck draws a sharp distinction between jihadist theology and traditional interpretations of Islam, she notes that jihadist ideas "did not spring from a void, nor are all of them the marginal opinions of a few fanatics." For example, the scholar Ibn Taymiya (d. 1328), who is widely respected in Muslim circles, lived when the Mongols ruled over the Islamic world. Although they claimed to be Muslims, the Mongols' system of laws was based on their native customs rather than Islamic law (sharia).

Disturbed by this situation, Ibn Taymiya argued that the Islamic faith requires state power because the Koran only says that Muslims are the "best community" when they "enjoined the good and forbade the evil." In failing to base their legal system on Islamic law, the Mongols disregarded that Koranic injunction. Thus, Ibn Taymiya said that Muslims were required to take up arms against the Mongols.

Contemporary jihadists liken the modern rulers of the Muslim world to the Mongols. And there are scholars beside Ibn Taymiya to whom they can look for inspiration, including Abdul Wahhab and the three major jihadist thinkers of the twentieth century: Hassan al-Banna, Sayyid Abul A'la Maududi and Sayyid Qutb.

DRAWING UPON AN IMPRESSIVE ARRAY of primary-source material from these and like-minded Islamic radicals, Habeck makes her greatest contribution by illuminating the building blocks of the jihadist worldview.