On February 18th, as part of the official recognition of Black History Month, President Obama met with a group of African-American leaders at the White House to discuss civil-rights issues. The guests—who included Representative John Lewis, of Georgia; Sherrilyn Ifill, the director-counsel of the N.A.A.C.P. Legal Defense and Educational Fund; and Wade Henderson, who heads the Leadership Conference on Civil and Human Rights—were intent on pressing the President to act decisively on criminal-justice issues during his last year in office. Their urgency, though, was tempered by a degree of sentimentality, verging on nostalgia. As Ifill later told me, “We were very much aware that this was the last Black History Month of this Presidency.”

But the meeting was also billed as the “first of its kind,” in that it would bring together different generations of activists. To that end, the White House had invited DeRay Mckesson, Brittany Packnett, and Aislinn Pulley, all of whom are prominent figures in Black Lives Matter, which had come into existence—amid the flash points of the George Zimmerman trial; Michael Brown’s death, in Ferguson, Missouri; and the massacre at the Emanuel A.M.E. Church, in Charleston, South Carolina—during Obama’s second term.

Published in the print edition of the March 14, 2016, issue.

Black Lives Matter has been described as “not your grandfather’s civil-rights movement,” to distinguish its tactics and its philosophy from those of nineteen-sixties-style activism. Like the Occupy movement, it eschews hierarchy and centralized leadership, and its members have not infrequently been at odds with older civil-rights leaders and with the Obama Administration—as well as with one another. So it wasn’t entirely surprising when Pulley, a community organizer in Chicago, declined the White House invitation, on the ground that the meeting was nothing more than a “photo opportunity” for the President. She posted a statement online in which she said that she “could not, with any integrity, participate in such a sham that would only serve to legitimize the false narrative that the government is working to end police brutality and the institutional racism that fuels it.” Her skepticism was attributable, in part, to the fact that she lives and works in a city whose mayor, Rahm Emanuel, Obama’s former chief of staff, is embroiled in a controversy stemming from a yearlong coverup of the fatal shooting by police of an African-American teen-ager.

Mckesson, a full-time activist, and Packnett, the executive director of Teach for America in St. Louis, did accept the invitation, and they later described the meeting as constructive. Mckesson tweeted: “Why did I go to the mtg w/ @POTUS today? B/c there are things we can do now to make folks’ lives better today, tomorrow, & the day after.” Two weeks earlier, Mckesson had announced that he would be a candidate in the Baltimore mayoral race, and Obama’s praise, after the meeting, for his “outstanding work mobilizing in Baltimore” was, if not an endorsement, certainly politically valuable.

That split in the response to the White House, however, reflected a larger conflict: while Black Lives Matter’s insistent outsider status has allowed it to shape the dialogue surrounding race and criminal justice in this country, it has also sparked a debate about the limits of protest, particularly of online activism. Meanwhile, internal disputes have raised questions about what the movement hopes to achieve, and about its prospects for success.

The phrase “black lives matter” was born in July of 2013, in a Facebook post by Alicia Garza, called “a love letter to black people.” The post was intended as an affirmation for a community distraught over George Zimmerman’s acquittal in the shooting death of seventeen-year-old Trayvon Martin, in Sanford, Florida. Garza, now thirty-five, is the special-projects director in the Oakland office of the National Domestic Workers Alliance, which represents twenty thousand caregivers and housekeepers, and lobbies for labor legislation on their behalf. She is also an advocate for queer and transgender rights and for anti-police-brutality campaigns.

Garza has a prodigious social-media presence, and on the day that the Zimmerman verdict was handed down she posted, “the sad part is, there’s a section of America who is cheering and celebrating right now. and that makes me sick to my stomach. we GOTTA get it together y’all.” Later, she added, “btw stop saying we are not surprised. that’s a damn shame in itself. I continue to be surprised at how little Black lives matter. And I will continue that. stop giving up on black life.” She ended with “black people. I love you. I love us. Our lives matter.”

Garza’s friend Patrisse Cullors amended the last three words to create a hashtag: #BlackLivesMatter. Garza sometimes writes haiku—she admires the economy of the form—and in those four syllables she recognized a distillation not only of the anger that attended Zimmerman’s acquittal but also of the animating principle at the core of black social movements dating back more than a century.

Garza grew up as Alicia Schwartz, in Marin County, where she was raised by her African-American mother and her Jewish stepfather, who run an antiques store. Her brother Joey, who works for the family business, is almost young enough to have been Trayvon Martin’s peer. That is one reason, she says, that the Zimmerman verdict affected her so deeply. The family was not particularly political, but Garza showed an interest in activism in middle school, when she worked to have information about contraception made available to students in Bay Area schools.

She went on to study anthropology and sociology at the University of California, San Diego. When she was twenty-three, she told her family that she was queer. They reacted to the news with equanimity. “I think it helped that my parents are an interracial couple,” she told me. “Even if they didn’t fully understand what it meant, they were supportive.” For a few years, Garza held various jobs in the social-justice sector. She found the work fulfilling, but, she said, “San Francisco broke my heart over and over. White progressives would actually argue with us about their right to determine what was best for communities they never had to live in.”

In 2003, she met Malachi Garza, a gregarious, twenty-four-year-old trans male activist, who ran training sessions for organizers. They married five years later. In 2009, early on the morning of New Year’s Day, a transit-police officer named Johannes Mehserle fatally shot Oscar Grant, a twenty-two-year-old African-American man, in the Fruitvale BART station, in Oakland, three blocks from where the Garzas live. Alicia was involved in a fight for fair housing in San Francisco at the time, but Malachi, who was by then the director of the Community Justice Network for Youth, immersed himself in a campaign to have Mehserle brought up on murder charges. (He was eventually convicted of involuntary manslaughter, and served one year of a two-year sentence.)

Grant died nineteen days before Barack Obama’s first Inauguration. (The film “Fruitvale Station,” a dramatic recounting of the last day of Grant’s life, contrasts his death with the national exuberance following the election.) His killing was widely seen as a kind of political counterpoint—a reminder that the grip of history would not be easily broken.

Garza had met Patrisse Cullors in 2005, on a dance floor in Providence, Rhode Island, where they were both attending an organizers’ conference. Cullors, a native of Los Angeles, had been organizing in the L.G.B.T.Q. community since she was a teen-ager—she came out as queer when she was sixteen and was forced to leave home—and she had earned a degree in religion and philosophy at U.C.L.A. She is now a special-projects director at the Ella Baker Center for Human Rights, in Oakland, which focusses on social justice in inner cities. Garza calls Cullors her “twin.” After Cullors created the Black Lives Matter hashtag, the two women began promoting it. Opal Tometi, a writer and an immigration-rights organizer in Brooklyn, whom Garza had met at a conference in 2012, offered to build a social-media platform, on Facebook and Twitter, where activists could connect with one another. The women also began thinking about how to turn the phrase into a movement.

DeRay Mckesson has announced that he is running for mayor of Baltimore. Photograph by Christaan Felber

Black Lives Matter didn’t reach a wider public until the following summer, when a police officer named Darren Wilson shot and killed eighteen-year-old Michael Brown in Ferguson. Darnell Moore, a writer and an activist based in Brooklyn, who knew Cullors, coördinated “freedom rides” to Missouri from New York, Chicago, Portland, Los Angeles, Philadelphia, and Boston. Within a few weeks of Brown’s death, hundreds of people who had never participated in organized protests took to the streets, and that campaign eventually exposed Ferguson as a case study of structural racism in America and a metaphor for all that had gone wrong since the end of the civil-rights movement.