In Atlanta, about 200 young demonstrators sat down in the middle of Peachtree Street, not far from the annual Martin Luther King Jr. Day commemoration at Ebenezer Baptist Church, and briefly stopped the parade.

In St. Louis, a group of protesters rushed the stage at a prayer service, bringing the event to a halt until police arrived.

In New York, there was a "die-in" outside Bloomingdale’s, in the heart of an upscale shopping area, while in Boston, similar "die-ins" took place on streets between Boston Common and the Public Garden and then in front of the State House.

The nation’s celebration of King’s birthday Monday was punctuated by protest this year, as a new generation of young activists, angered by the deaths of several unarmed African-Americans in confrontations with police, demanded that the traditional rituals of speechmaking, community service, and prayer breakfasts give way to denunciations of injustice and inequality.

"The events that have happened have kind of diminished his dream a little bit," said Aleah Hutchinson, 17, who attended the King Day parade in Athens, Ala., and won a local essay contest about King. "He wanted us all to work together in unity, but when certain events occur, like the events in Ferguson and the Trayvon Martin case, it kind of diminishes his dream a little bit because at that point, we’re not working together."

In Atlanta — where the holiday has for years been a big but generally mellow and celebratory affair — a showdown occurred between the civil rights old guard and the new, more boisterous generation of protesters, many of whom were catalyzed to action by the deaths of Michael Brown in Ferguson, Mo., and Eric Garner in New York, both at the hands of the police.

The protesters argued that the holiday had become corrupted by corporate involvement, diluting King’s ideas — about economics as well as race. So with signs, slogans, and shouts, they inserted themselves into the annual parade as it made its way down Peachtree Street, Atlanta’s downtown thoroughfare. Several times, the group sat and lay en masse in the middle of the street, raising fists toward the air as police pleaded with them to move on.

"We’re going to reclaim MLK’s holiday!" an activist and author, Aurielle Marie, 20, yelled at the Atlanta protest. "We will not allow those that actively subject us to an oppressive lifestyle to lead the parade or be in the parade."

In front of Ebenezer Baptist Church, where King and his father both preached, protesters marched to the front of a stage, where a service was underway. Carrying a cardboard box decorated like a coffin, and demanding to be heard, they chanted "Black people are dying."

Organizers of the official commemoration seemed both frustrated and accommodating, allowing the demonstrators to take the podium, for a time, during which one young man declared that he had enough of "the MLK they shove down our throats."

K. Renee Robertson, of the Southern Christian Leadership Conference, said afterward that she thought the insurgents’ passion was "great."

"But do it in the right way," Robertson said.

Similar events unfolded in St. Louis, where several thousand people marched from the city’s Old Courthouse, where enslaved blacks were once sold as property, to Harris-Stowe State University, where the marchers joined a packed auditorium for an interfaith service.

As a musical act took the stage, a couple of dozen demonstrators ran up and seized the microphone, where one young man shouted, "St. Louis PD, KKK, how many kids did you kill today." About a dozen St. Louis Police officers helped university security officers clear the stage.

"The difference this year is that people are more energized," said Missouri state Senator Jamilah Nasheed, D-St. Louis, who has been involved in the Ferguson protests. "They are ready to rise up and promote change."

One of the day’s larger gatherings was in Philadelphia, where thousands marched peacefully through the city center, calling for an end to a stop-and frisk policy by city police; higher funding for cash-starved public schools, and an increase in the minimum wage.

"This is to make people aware that it’s not just a day of service," said Wesley Wilson-Bey, 68, at a rally outside the headquarters of the school district. "People have relegated Dr. King to just cleaning floors and all that kind of stuff on this day, and that’s not what he was. He was a person who made things happen."

More than 1,000 people gathered in New York; across the plaza, a banner reading "Black Lives Matter" was suspended from the front of a church. Demonstrators, some carrying signs demanding justice for Garner and Brown, marched down Lexington Avenue, accompanied by a mobile system broadcasting King’s speeches.

"Martin Luther King’s dream hasn’t been realized yet," said Norell Edwards, 23, a graduate student from Washington, who joined the protesters in New York. "This is a way to try to finish his work and stand together with unity and equality."

In Boston, where hundreds gathered, march organizers said they wanted criminal justice reforms, a $15 per hour minimum wage, and an end to efforts to bring the 2024 Olympics to town, among other demands.

Lena Zuckerwise, 35, a senior lecturer in political science at Simmons College, carried a sign that read "Dr. King was no moderate/Shut it down."

"There is a perception that what Martin Luther King, Jr., was doing was honorable, and what we are doing today is disruptive," said Zuckerwise. She added, "I think it’s a historical falsehood, that there were profound differences between what Martin Luther King and others were doing at the time and what we’re trying to accomplish here."

Smaller crowds gathered in Chicago, where more than 100 protesters marched down the sidewalks of the upscale Magnificent Mile shopping district and to the Board of Trade, and in Washington, where about 100 gathered in front of the White House.

"Just seeing the recent news with unarmed civilians being shot by the police, it’s an obvious injustice," said Denisha Burns, 33, in Chicago, where protesters recited the names of people killed by police.

In Washington, as 16-year-old Ananda Ewing-Boyd sang "A Change is Gonna Come," organizers passed out lists of demands, including an end to violence by the police, and raised money for local homeless shelters.

"Part of the idea is reminding people what MLK Day is about," said Caroline Tyson, a 19-year-old college student. "It’s not just a day off work."

Even in small towns, the events of recent years affected the celebrations. In Athens, Alabama, where a column of junior ROTC cadets and the mayor led an annual parade past Limestone Drug and the U.G. White Mercantile, some marchers wore black shirts with the names of Michael Brown, Eric Garner and Trayvon Martin, as well as Wenjian Liu and Rafael Ramos, the two New York City police officers who were shot to death as they sat in their patrol car.

"We’ve got to break the cycle of the past," said Lionel Turner, a 38-year-old marcher. "There used to be slave masters and stuff like that, but now it’s changed to organized police officers, and they find a way within the law to break the law themselves. You’ve got to find some kind of way to unify everyone."

Michael Paulson, New York Times