Rancor toward the Stanton-Anthony brigade began building almost from the start. Firestone’s tendency to be dismissive of others’ grievances didn’t help, nor did her intensity. At a famous demonstration in which a hundred women rallied at the Ladies’ Home Journal offices to protest the publication’s sexist content and hiring practices, Firestone jumped on the desk of the editor-in-chief, John Mack Carter, and tore up copies of the magazine in his face. Her detractors accused her of homicidal tendencies.

“The group is falling apart,” Firestone wrote to Laya on May 26, 1970, and confessed to “a little bit of a sleepless night.” She added, “Basically, I don’t believe finally that the revolution is so imminent that it’s worth tampering with my whole psychological structure, submitting to mob rule, and so on, which is what they’re all into.” Some days later, the members of New York Radical Feminists gathered in a hall downtown for a general meeting. The West Village-1 group aired its complaints, women began shouting at one another, and then they voted overwhelmingly to abolish the structure that Firestone had crafted. The Stanton-Anthony brigade retreated to the cellar, where Firestone and Koedt announced their resignations and left the hall. All but two of the Stanton-Anthony members quit soon thereafter, and Koedt withdrew from activism. “I was done with groups after that,” she told me.

Brownmiller declined to talk to me about the incident, referring me to her memoir, “In Our Time” (1999), which claims only that Firestone “abruptly quit her fourth creation, New York Radical Feminists, after a split over leadership inside her Stanton-Anthony brigade.” John Duff, a sculptor who was Firestone’s on-again, off-again boyfriend in this period, remembers Firestone telling him that she had been forced out by an “anti-leadership” faction. “And guess who became the new leaders?” she said to him. “The anti-leaders.” Late on the night of the vote, Firestone showed up at Anne Forer’s door. Forer remembers her saying, “They threw me out and that’s it.”

The dissolution of New York Radical Feminists coincided with the movement’s first mainstream publishing successes. Kate Millett’s “Sexual Politics,” Firestone’s “Dialectic,” and “Sisterhood Is Powerful,” an anthology edited by Robin Morgan, all sold well and were widely covered by the media. (Millett was on the cover of Time.) But, by the time “Dialectic” appeared in bookstores, in October, 1970, Firestone was half a year into her self-exile from the movement. In the copy she sent to Laya, she wrote, “To Laya, the only true sister, after all.”

Brownmiller wrote in her memoir that Firestone wanted her book to “place her in the firmament next to Simone de Beauvoir. She watched the media circus engulfing Kate and champed at the bit, awaiting her turn.” Others recall the opposite. Firestone had already been denounced by feminists for violating the “We’re all equals” ethic by accepting a book advance—of less than two thousand dollars—and for appearing on “The David Susskind Show.” James Landis, Firestone’s editor at William Morrow, remembers with amazement that “she came to me quite troubled and said that the women in whatever group it was wanted to own the copyright. I told her, ‘Forget it!’ ”

Instead, at the last minute, she slowed the book’s production with a flurry of small corrections. She explained why in her roman à clef: “She thought of Anne Moffitt”—her pseudonym for Millett—“as a decoy, to deflect the klieg light.” Her fears proved to be founded. The attention accorded the publication of “Sexual Politics” provoked an instant backlash within the movement as well as outside it. The emerging lesbian wing browbeat Millett into revealing that she was bisexual, and then denounced her for not having revealed it earlier. Millett had a breakdown and was committed to a mental hospital. In “Flying” (1974), she recalls a dream she had at the time, in which “figures of women ranged about a room question and cut at my life.”

Meanwhile, “Dialectic” was stoking a small revolution at the Morrow offices. The female employees began asking questions: Why were all the secretaries and publicists women? Why were the few female editors underpaid? “We started having lunchtime meetings behind closed doors,” Sara Pyle, an assistant in the publicity department at the time, told me. “We all stopped wearing our little heels and skirts.” What made the women at Morrow “go a bit nuts,” Pyle said, was the book’s unvarnished radicalism. “Firestone took Marx further and put women in the picture,” she said. “This was our oppression, all laid out.” And not just women’s oppression. The book’s longest chapter, “Down with Childhood,” chronicled the ways that children’s lives had become constrained and regulated in modern society. “With the increase and exaggeration of children’s dependence, woman’s bondage to motherhood was also extended to its limits,” Firestone wrote. “Women and children were now in the same lousy boat.” The argument drew the appreciation of one notable feminist, which must have pleased Firestone. Simone de Beauvoir told Ms. that only Firestone “has suggested something new,” noting how the book “associates Women’s Liberation with children’s liberation.”

The liberator for Firestone was the right to be loved for oneself, not as part of a patronage system “to pass on power and privilege.” She was trying to imagine a “home” where “all relationships would be based on love alone,” a world, to quote the last words of the book, that allows “love to flow unimpeded.” When “Dialectic” was published, Firestone’s sister Tirzah said, their father called it “the joke book of the century,” and refused to read it.

In 1970, in a contribution to Notes from the Second Year, titled “Woman and Her Mind,” Meredith Tax argued that the condition of women constituted a state of “female schizophrenia”—a realm of unreality where a woman either belonged to a man or was “nowhere, disappeared, teetering on the edge of a void with no work to do and no felt identity at all.” By mid-century, Elaine Showalter noted, in “The Female Malady” (1985), scores of literary and journalistic works had defined schizophrenia as a “bitter metaphor” for the “cultural situation” of women. It was this state of affairs that the radical feminists had set out to change, only to find themselves doubly alienated. The first alienation was a by-product of their political vision: radical insight can resemble the mind-set described by the clinical psychologist Louis Sass, in “Madness and Modernism” (1992), when he wrote that the schizophrenic is “acutely aware of the inauthenticities and compromises of normal social existence.” The second alienation was tragic: alienation from one another.

Medical researchers have long puzzled over schizophrenia’s late emergence (it was first diagnosed in 1911, in Switzerland) and its prevalence in the industrial world, where the illness is degenerative and permanent. (In “primitive” societies, when it exists at all, it is typically a passing malady.) In 2005, when Jean-Paul Selten and Elizabeth Cantor-Graae, experts on the epidemiology of schizophrenia, reviewed various risk factors—foremost among them migration, racism, and urban upbringing—they found that the factors all involved chronic isolation and loneliness, a condition that they called “social defeat.” They theorized that “social support protects against the development of schizophrenia.”

The second-wave feminists had hoped to alleviate this isolation through the refuge of sisterhood. “We were like pioneers who’d left the Old Country,” Phyllis Chesler, a feminist psychologist and the author of “Women and Madness” (1972), told me. “And we had nowhere to go back to. We had only each other.” That is, until the movement’s collapse. Last fall, as I interviewed New York’s founding radical feminists, the stories of “social defeat” mounted: painful solitude, poverty, infirmity, mental illness, and even homelessness. In a 1998 essay, “The Feminist Time Forgot,” Kate Millett lamented the lengthening list of her sisters who had “disappeared to struggle alone in makeshift oblivion or vanished into asylums and have yet to return to tell the tale,” or who fell into “despairs that could only end in death.” She noted the suicides of Ellen Frankfort, the author of “Vaginal Politics,” and Elizabeth Fisher, the founder of Aphra, the first feminist literary journal. “We haven’t helped each other much,” Millett concluded. We “haven’t been able to build solidly enough to have created community or safety.”