The steps that placed the United States on a war footing after Sept. 11, 2001, responded to a threat that had been building, and killing, for decades. In the late 1940s, Sayid Qutb, an Egyptian civil servant, came to placid Greeley, Colo., on a traveling fellowship and was mortified at what he saw as the decadence and spiritual hollowness of American life — the music, the hair styles, the mixing of the sexes even in church. He returned to Egypt, joined the Muslim Brotherhood and spent the rest of his life, which terminated at the end of a Nasser regime hangman’s rope in 1966, teaching that the duty of Muslims is to extinguish Western civilization. His followers found refuge in Saudi Arabia, and his brother, Mohammed, taught the doctrine to many, including the Egyptian who is now the leader of al-Queda, Ayman al-Zawahiri, and his predecessor, then the pampered child of a wealthy Saudi family, Osama bin Laden.

The doctrine sparked visibly in this country with the assassination of Meir Kahane, a right-wing Israeli politician, in a New York hotel in 1990, by El-Sayid Nosair, and flared again with the first World Trade Center bombing in 1993, undertaken in part to free Nosair from jail, with the spiritual authorization of Omar Abdel Rahman, the so-called “blind sheikh,” who had been Nosair’s spiritual mentor. In 1996, and again in 1998, bin Laden declared that militant Muslims were at war with the United States. Then came the near-simultaneous bombing of U.S. embassies in Kenya and Tanzania in 1998, with a death toll in the hundreds, and the bombing of the U.S.S. Cole in Aden, Yemen, in 2000, that killed 17 sailors.