A century ago, if you had said that evangelical Christianity would one day emerge as a leading political force in America, you might have met incredulity or even ridicule. Such belief was widely seen as a throwback to the old days of snake handling and speaking in tongues. Didn’t Clarence Darrow prove definitively, after all, in a Tennessee courtroom that Americans were ready for the science of the future in the place of the religion of the past?

But something happened along the way. Radicalized by the culture wars of the 1960s and ’70s, offended by the sexual revolution, energized by the rise of modern conservatism in the 1980s, and with a rural tradition of local sovereignty, evangelical Christianity found its voice as a political movement.

That movement is not monolithic. As the noted journalist and historian Frances FitzGerald observes in her new book The Evangelicals: The Struggle to Shape America, although evangelical Christians have largely tended to the political right, “their world is decentralized and difficult to lead, much less to control.”

FitzGerald, perhaps best known for her Pulitzer Prize–winning 1972 book, Fire in the Lake: The Vietnamese and the Americans in Vietnam, has long been interested in American sectarianism. In her 1986 book, Cities on a Hill, she introduced readers to a fairly new arrival on the political scene of one evangelical leader, Jerry Falwell, who built a church in the mountain country of southwestern Virginia by preaching one to one, going door to door, painstakingly building an audience of the disaffected and needful.

Her account was prescient. Thirty-odd years later, and even a decade after his death, Falwell’s congregational empire continues to grow, embracing megachurches, a major private university, and a sizable segment of what came to be branded Moral Majority. Franklin Graham, Pat Robertson, Joel Osteen, the list goes on, adding up to a huge force that is as much secular as it is spiritual.

“I wrote about the birth of the Moral Majority,” FitzGerald says, “and then I quit and went back to it, and quit again to write other books. Finally, I thought, well, this really is very important to our history, and I’d better report it and know it. So I started from the beginning and built my story chapter by chapter.”

The result is a sprawling book that FitzGerald smilingly calls a “toe-breaker,” one that reaches back to the Protestant schisms of two and three centuries past, recounting the rejection of established authority and of religious formalism and intellectualism in favor of personal experience to build, as FitzGerald puts it, “a religion of the heart, as opposed to the head.”

“After the Scopes trial,” FitzGerald says, “everyone said that the fundamentalists were dead and gone. They were thriving, with an extraordinary group of characters who pushed the movement forward. The whole idea was to defeat the modernists, a struggle that was not well documented. Certainly a lot of it was unknown to me before I began this book.”

That struggle, she notes, has pitted liberal and conservative evangelicals against each other, and it has involved making devil’s bargains with politicians who might not always share evangelical ideals—the sitting president, say, who publicly cited the Bible as his favorite book but, FitzGerald writes, “did not seem to remember even a verse of it.”

Journalists have covered evangelicals, observes FitzGerald, with a combination of sensationalism and neglect. Certainly her book, toe-breaker that it is, merits no such label. Careful and evenhanded, it describes a segment of American society and political culture that is much with us today—and one that will be with us for a long time to come.

Gregory McNamee is a contributing editor.