The Passion of Dr. Martin Luther King Jr.

Martin Luther King Jr., left, and Stokely Carmichael participate in a voter registration march in 1966. King was felled by an assassin’s bullet 47 years ago in Memphis, Tennessee. Lyyn Pelham/The LIFE Picture Collection/Getty

Martin Luther King Jr. was felled by an assassin's bullet 47 years ago in Memphis, Tennessee. King's life came to an end that Thursday, April 4, 1968, yet his legacy would live on in ways that surpass historical imagination and comprehension. In our contemporary political and cultural landscape King has achieved the kind of towering legacy that both elevates and at times distorts his actual political achievements, his genuine successes and failures. It's worth remembering that King—celebrated with a national holiday and a memorial in Washington, D.C., and lauded as a "Founding Father" worthy of a place in a national pantheon that includes presidents Washington, Lincoln and Jefferson—was not a president but a social movement leader, one whose political trajectory grew increasingly radical even as his time on Earth was growing shorter.

We celebrate MLK in Selma and at the March on Washington but stay largely silent about his anti-war and anti-poverty activism, which revealed the ambitions and limits of his dream of a beloved community.

Those limits came into sharpest focus in the aftermath of one of King's greatest political triumphs. Political turmoil in Selma, Alabama in 1965 riveted the nation, turning into one of the most indelible chapters in America's racial history and leading to the passage of the Voting Rights Act on August 6, 1965. President Lyndon Johnson signed the voting bill and gave a beaming King a commemorative pen.

Five days later the Watts neighborhood in Los Angeles exploded in what would be a week-long riot that represented the largest domestic civil unrest in the nation's history. Watts transformed King, who was heckled by local residents for preaching nonviolence. He would spend the next three years connecting issues of racial equality to a movement for economic justice and ending the Vietnam War.

The Black Power Movement, popularized by the young activist Stokely Carmichael, forced King to confront the limits of the political reforms advocated by the civil rights movement. Voting rights and unfettered access to public accommodations did little to tackle the stubbornness of income inequality and the yawning wealth gap between the races. Public school integration remained halting and unsteady. Against this sobering backdrop some African-Americans grew more radicalized even as many whites became disaffected with what seemed like a seemingly endless list of racial grievances that now spilled over into a wave of domestic racial uprisings.

King faced the onslaught of white backlash and Black Power by linking domestic struggles for racial justice with an international vision for human rights that challenged America to direct resources being spent in Vietnam to the domestic war on poverty. For King, Lyndon Johnson's dreams of a Great Society would not be achieved through guns and butter.

On April 4, 1967, one year before his death, King publicly denounced the Vietnam War during a speech at New York's Riverside Church. Declaring that the "time for silence" had passed, King thrust himself into the forefront of the nation's burgeoning anti-war movement, an act that effectively ended his political alliance with Johnson.

Martin Luther King, Jr. addresses an audience at the Palais des Sports in Paris, France, on March 29, 1966. AFP/Getty

King's last year on Earth featured daring political alliances. Eleven days after his Riverside address King and Carmichael shared a stage at a huge anti-war demonstration that ran from Central Park to the United Nations. Carmichael and King, despite political disagreements on the question of self-defense and nonviolence, found common ground in opposing the war in Vietnam.

Two weeks later King personally invited Carmichael to Atlanta's Ebenezer Baptist Church, where Stokely led the standing ovation after King's most forceful anti-war speech to date.

The radical King expressed disappointment over the billions of dollars being spent in Vietnam, funds he insisted were being diverted from the war on poverty. As a response King ignited a Poor People's Campaign, a sprawling effort that attracted welfare rights organizers, poor whites, Native Americans, Latinos and African-Americans who vowed to erect a tent city (which would be called "Resurrection City") in Washington until the Congress passed comprehensive legislation guaranteeing every American income or a job.

King never lived to see Resurrection City in full bloom. A man feted by the international community, who dined with royalty and consorted with the American president, spent his final hours aiding garbage workers fighting for a living wage.

King's final speech, on April 3, 1968 in Memphis, Tennessee, is most often remembered (like his March on Washington address) for its poetic conclusion, when he preached about traversing the "mountaintop" and witnessing the "promised land" of racial and economic justice that awaited African-Americans. "We've got some difficult days ahead of us," he reminded them, but he remained boldly optimistic that justice would come. Perhaps the most important part of that speech is a moment that is largely forgotten. "The greatness of America," said King, "lies in the right to protest for right."

King's political courage at the end of his life found him on the wrong side of sitting American presidents, mainstream liberal thought leaders and the national racial status quo. Remarkably, King tapped into what he characterized as "those great wells of democracy" to reveal the depth and breadth of racial and economic injustice despite America's insistence that civil rights laws had ushered in a new age of citizenship and justice.

But, like contemporary #BlackLivesMatter demonstrators, King insisted that the diminishment of racial and economic oppression did not equal full and robust citizenship. King believed that black lives mattered—not only at the voting booths and in restaurants and public accommodations, but for those who collected garbage, lived off of food stamps and could barely afford to keep a roof over their heads.

This kind of moral and political conviction transcended the soaring rhetoric for which the early King is most remembered. Having shared his vision of a beloved community with the world during most of his career, King spent the rest of his life (and all of his political capital) on matching eloquent words with heroic deeds in the face of daunting odds. Forty-seven years after his death, it is worth remembering the radical Martin Luther King Jr. who demanded a "revolution of values" long after the national applause had stopped.

Peniel E. Joseph is a professor of history and founding director of the Center for the Study of Race and Democracy at Tufts University. He can be followed on twitter @penieljoseph.