(RNS) — Two years ago, Pope Francis denounced what he called “a very strong, organized, reactionary attitude” within the American Catholic church. To his successor, and anyone who wants to understand how this attitude has shaped the church, I recommend “Catholic Fundamentalism in America,” a new book by the Rev. Mark S. Massa.

Massa is a Jesuit priest who teaches American religious history and runs the Boisi Center for Religion & American Public Life at Boston College. (Full disclosure: I’m on the board of advisers.) He does not use the term fundamentalist as a loose pejorative. In his analysis, Catholic fundamentalism mirrors the Protestant fundamentalism of a century ago in its primitivism and sectarianism.

That’s to say, Catholic fundamentalists, like their Protestant forebears, see themselves as restoring an old-time religion in opposition to the liberal tendencies of the leaders of their tradition, whom they disdain. Like the Protestant fundamentalists, too, they are culture warriors who use apocalyptic rhetoric to assail liberal trends in society at large.

Massa traces this strain in American Catholicism back to what’s been called the “comic opera heresy” of a fellow Jesuit, Leonard Feeney.

After World War II, Feeney became the leader of a Catholic student center a block from Harvard Yard in Cambridge, Massachusetts. A charismatic speaker, he attracted converts from the university, which he took to denouncing as an engine of secularism and corrupt social values. He also took to denouncing the Archdiocese of Boston, which in his eyes had given up on the ancient principle of “no salvation outside the church.”

After being excommunicated and kicked out of his order, he established his followers — styled as “The Slaves of the Immaculate Heart of Mary” — as an irregular Catholic commune 30 miles west of Cambridge.

As minor a role as the Feeneyites played in postwar American Catholicism, their adversarial stance toward the church hierarchy and the world (as well as the celebrity they enjoyed in their heyday) provides Massa with a template for identifying subsequent fundamentalist Catholic undertakings. These include Gommar DePauw‘s Catholic Traditionalist Movement of the post-Vatican II years, dedicated to restoring the Latin Mass; EWTN (the Eternal World Television Network), which Mother Angelica founded in the early 1980s and made into a sharp critic of progressive church leaders; and the community of St. Marys in Kansas, associated with the schismatic Society of St. Pius X, which grew up at the same time.

Also: Christendom College in Virginia, whose educational program is dedicated to fostering the ideal of America as a Catholic-led country; ChurchMilitant.com, whose mission was to denounce the gay subculture in the church and in American society generally; and Crisis magazine, a onetime journal of sophisticated Catholic opinion that became an apocalyptic assailant of Pope Francis.

Disparate these undertakings may be, but Massa makes a strong case that, by meeting his fundamentalist criteria, they deserve to be grouped into a single movement — some devoted to creating a separate Catholic subculture, others to transforming the United States into one nation under their church. The religion they idealize predates the Second Vatican Council — in some cases, the urban Catholicism of the early 20th century; in others, the Western Christianity of the High Middle Ages.

All have been arrayed against one or another of the reforms of Vatican II, be it liturgy in the vernacular or acknowledgment of other faiths or acceptance of church-state separation. It is above all the sectarianism implicit in their rejection of Vatican II, as well as the post-Vatican II papal magisterium that, for Massa, earns them the fundamentalist label.

This, more than anything else, sets them apart from the Protestant fundamentalists of yore. Because Protestantism has from the beginning been all about establishing your own religious institutions, Protestant fundamentalists simply created churches and denominations to replace those they couldn’t take over. For Catholic fundamentalists, to break faith with the church hierarchy is to break faith with, well, the faith.

A few separate from the church, either voluntarily or by ecclesiastical edict, but most stay in. And because one or more of their passions has resonated in the wider, conservative Catholic world, they’ve always had their fellow travelers, their secret and not-so-secret supporters, their intellectual co-conspirators. While Massa is careful to avoid broad accusations, he does not hesitate to name some names.

These include big funders like Timothy Busch, neo-integralist professors like Patrick Deneen and Adrian Vermeule, and hierarchs such as Cardinal Raymond Burke and Archbishop Charles Chaput. Call them traditionalists if you like, but they toll the bell of Catholic fundamentalism. And on websites like ChurchMilitant and on the hugely popular EWTN, they display it to a wider Catholic public.

To be sure, the conservative attitude animating the American church draws on nonfundamentalist sources. But Massa’s book goes a long way toward explaining the fundamentalist strain that, once delineated for the reader, will never seem anything but obvious.