Knowing one's adversary, according to Sun Tzu, the author of "The Art of War," is a prerequisite for victory. Costly missteps in the war on terror, especially the invasion of Iraq, suggest that the Bush administration doesn't grasp al-Qaida's ideology. As a result, the United States, though scoring short-term tactical victories against the jihadists, all too frequently furthers Osama bin Laden's long-term strategic aims. A deeper understanding of al-Qaida's philosophy would help the United States gain the initiative in the war of ideas. In the aftermath of Sept. 11, the Bush administration settled on a simple narrative to explain why...