Under Benedict, the rapport between nuns and the Vatican has been strained, to say the least. Last spring a rare public rift opened between the Church hierarchy and the largest group of American nuns, the Leadership Conference of Women Religious. The Vatican accused the sisters of insufficient orthodoxy and deference to bishops, openness to “certain radical feminist themes incompatible with the Catholic faith,” and neglecting traditional social issues such as opposition to abortion and gay marriage. This “doctrinal assessment,” the result of an investigation begun in 2008, took the unprecedented step of placing the nuns’ group under the command of three US bishops for five years. The LCWR released a statement saying it was “stunned.”

The rift came at a critical time for nuns. Today, there are just 56,000 left in the United States, down from a peak of 180,000 in 1965. (In Boston, the numbers have shrunk from more than 6,000 to about 1,750 over roughly the same period.) And the population that remains is graying quickly. A major 2009 report from the Center for Applied Research in the Apostolate found that 91 percent of “finally professed” nuns—those who have gone through a years-long trial period and made permanent vows—were 60 or older. In a momentous shift, the number of young women hearing the call to religious life is now smaller than the number of men: For the first time in American history, there are more future priests than future nuns in the pipeline.

Poignantly, this upheaval and decline also come at a moment when historians and other scholars are taking a fresh look at the role of nuns in American life, and finding that nuns’ contributions to the broad story of America have been, if anything, underappreciated. Nuns have served as the face of ­Catholicism to generations of Americans, and they’ve also been pioneers in health care, education, and social work—fields that may sound decidedly secular today, but whose development in the United States was profoundly shaped by the labor and influence of nuns. And, as those stories come under close examination, it’s becoming clear that the question of what’s next for nuns affects not just the inner workings of the church, but its future course in America.

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N uns take vows of poverty, chastity, and obedience, but within the constraints of those promises they have cut a remarkably entrepreneurial and adventurous path through American history. “If you’re a Catholic woman in American society between the early 19th century to the late 1960s, you had far more opportunities within church structures than outside them for education and meaningful work,” said Kathleen Sprows Cummings, a professor of American Studies at Notre Dame, and director of the Cushwa Center for the Study of American Catholicism. (Officially, the term “nun” refers to a ­sister who lives a cloistered life, but most Catholics—and this article—use the term colloquially to refer to any woman who has taken vows to belong to a religious order.)

The first nuns in America arrived in New Orleans in 1727 from France. Within three months, they had opened a boarding school for girls; some consider them the country’s first professional elementary school teachers. As waves of immigration made a chiefly Protestant nation more Catholic, nuns spread accordingly. Nuns, many immigrants themselves, served as a kind of de facto social service agency for America’s great waves of newcomers, administering settlement houses, orphanages, and schools that served the poor.

In the decades that followed, American nuns built schools wherever they went, eventually staffing the largest parochial school system in the world. They were also leaders in higher education: By the 1950s, before coeducation began to transform American colleges, more American women were getting degrees from Catholic women’s colleges than from Protestant or nondenominational institutions.