Martin Luther King died 50 years ago

At the end of his life, Martin Luther King Jr. lamented that his dream had "turned into a nightmare."

When a shot killed his life while he was on the porch of a motel in Memphis, Tennessee, on April 4, 1968, the icon of the peaceful civil rights struggle in the United States was, at age 39, a man exhausted.

It was also a controversial figure, unlike what is celebrated today with a national holiday in the USA and with an imposing granite monument in Washington.

"It was frozen in time, not like the man he was in 1968, but his image in August 1963, when he gave his 'I have a dream' speech," comments David Farber, a professor of History at the University of Kansas.

"It's easy for Americans to forget how polarized King was in the 1960s," he says.

"He became a truly radical figure in the United States, a outspoken opponent of US foreign policy, who demanded justice not only for African Americans but for all poor Americans," he adds.

A turning point was the April 1967 speech in New York against the Vietnam War, a year in which more than 11,000 American soldiers died.

"King infuriated the entire civil rights movement, the government, and much of the political structure when it came out against the Vietnam War," said Henry Louis Taylor Jr., director of the University of Buffalo's Center for Urban Studies.

David Garrow, author of King's Bearing the Cross, said his opposition to the war was seen as "extremist" at a time when anti-war sentiment was "not very popular."

- In addition to civil rights -

At the time of his assassination by King James Earl Ray, a white man with racist ideas, King had been under constant surveillance for decades by the FBI, which had labeled him the "most dangerous" man in the country.

Her advocacy of nonviolence as a way to promote change was being challenged by a new generation of more impatient black activists.

"In the last 12 months of his life, King was very exhausted, very pessimistic, very depressed," Garrow said. "He said, a dozen times or more, in his last two years: 'The dream I had in Washington in 1963 turned into a nightmare.'"

"How much hatred, how much opposition did he face, and how part of it came in the form of horrible violence," says Political Science professor Jeanne Theoharis of CUNY Brooklyn College and author of "More Beautiful and Terrible History" of civil rights in the United States.

Fifty years after his death, the vision of racial equality that King claimed on the Lincoln Memorial staircase continues to spark debate.

Jason Sokol, a professor of history at the University of New Hampshire, says that, in those years, there were some advances for African Americans, with the victory of Barack Obama in 2008, becoming the country's first black president.

However, racial inequalities persist, "especially around black poverty, incarceration rate and police brutality," says Sokol, who also published a book on King's legacy, "The Heavens Might Crack."

Taylor, a professor at the University of Buffalo, points out that at the time of his death, King's ambitions "reveal the field of civil rights by pointing more to human rights."

"King imagined that another world was possible, grounded in economic, political and racial justice, things related to quality education, decent housing, good jobs," he explains.

"We have not really made much progress in the last 50 years in realizing his dream," he says.

"Although there have been changes in individual racial attitudes, racism embedded in US institutions and structures has not changed much," he added.

- Your legacy -

King's legacy can be noticed in many ways.

"In his 1964 Nobel Prize acceptance speech, King said the civil rights movement was the largest liberation movement in human history," recalls Taylor Branch, author of a trilogy about his life: "America in the King Years ".

"He was referring to the whole world, and not just to black people," he said.

And, "in many ways, it has been more successful than it could have imagined," Branch said, citing same-sex marriage, a black president in the United States, and women's rights.

King's legacy also appears in the "Black Lives Matter" movement against police violence and in others such as the one that recently convened the March for Our Lives, in which millions of young people took to the streets to demand tougher laws for the use of weapons, recalls the author.

"I am very optimistic that there is a new generation there that is picking up the notion of King's dreams," he said.

One of the participants in the march was King's granddaughter, Yolanda Renee, 9, who recalled her grandfather's most famous words to the crowd.

"I have a dream that is enough," said little Yolanda. "And that this must be a world free of weapons, period."