IN 1910, A COHORT of ultra-conservative American Protestants drew up a list of non-negotiable beliefs they insisted any genuine Christian must subscribe to. They published these “fundamentals” in a series of widely distributed pamphlets over the next five years. Their catalog featured doctrines such as the virgin birth, the physical resurrection of Christ, and his imminent second coming. The cornerstone, though, was a belief in the literal inerrancy of every syllable of the Bible, including in matters of geology, paleontology, and secular history. They called these beliefs fundamentals, and proudly styled themselves “fundamentalists” - true believers who feared that liberal movements like the social gospel and openness to other faiths were eroding the foundation of their religion.

Protestant fundamentalism was not an isolated impulse. The same tendency had already appeared in Catholicism; beginning with Pius IX, who issued his famous “Syllabus of Errors” in 1864, most popes severely condemned all liberal Catholic efforts. Muslims hate having the word “fundamentalist” applied to them, considering it a foreign term. Nonetheless, when some 19th-century Koran scholars sought to rethink their faith in the light of science and democracy, an angry opposition resisted these new ideas. Then, as European colonial powers tightened their grip on the region, other thinkers, like the Egyptian Sayyed Qutb, scorned any such reform efforts as imperialist pollution.

The expansion of religious fundamentalism in recent decades has been notable, as people around the world have sought certainty in the face of dizzying change. In the second half of the 20th century, old-time religion drew Americans jarred by their country’s setbacks in Korea and Vietnam, or disoriented by the civil rights movement and youth revolt of the 1960s. In Europe, American-style fundamentalism failed to make much progress, but highly conservative Catholic parties and groups, sometimes called “integralist,” gained strength in some countries. In the Muslim sphere, as oil funneled immense riches to the elite, it also drove hordes of village people into angry urban poverty. When secular solutions failed them, many were attracted to the promise of a more equal society based strictly on the Koran.

As the 20th century ended and a new one began, fundamentalism has taken on more formidable shapes, both politically and religiously. Though most of its adherents work through spiritual and educational channels, the small minority that turn to violence have caught the media’s attention. If some seem ready to die for faith, others are ready to kill for it, gunning down abortion doctors in church, hijacking planes, and exploding bombs at weddings. For plenty of thoughtful people, fundamentalism has come to represent the most dangerous threat to open societies since the fall of communism.