Martin Luther King's "I have a dream" speech may be the iconic symbol of the civil rights movement.
By Steve Schifferes
BBC News Online
And the March on Washington, which took place on 28 August, 1963, may be the apogee of the civil rights movement which transformed the lives of black Americans.
The fact that 250,000 demonstrators gathered peacefully to urge Congress to pass civil rights legislation was a milestone which catapulted the movement from a regional to a national impact.
Martin Luther King's speech is often seen as the overwhelming inspiration of the day
But it would take another president, and another year, before a major civil rights bill moved through Congress, then dominated by white southern Democrats.
And it would take another decade before black people would be able to acquire real political power in the South.
But, by then, the civil rights movement had fragmented amid violence and recriminations on all sides.
Grass roots movement
The momentum behind the March on Washington had been building for several years as the pace of civil rights activism increased following the Supreme Court decision in 1954 which outlawed segregation in public schools.
In 1956, Dr King had led the Montgomery bus boycott which had led to desegregation of the public transport system.
In 1960, young black college students across the South began a series of lunch counter sit-downs to force local stores to serve black people.
The young activists eventually joined forces with Dr King to form the Southern Christian Leadership Council (SCLC), and in early 1963 they turned their attention to desegregating the city of Birmingham, Alabama.
The momentum behind the march had been building for several years
The dramatic confrontations in April - with white police chief "Bull" Connor turning fire hoses on young demonstrators - brought the civil rights movement to national attention.
But President John F Kennedy was still reluctant to alienate southern white voters by pushing too hard for civil rights legislation.
So the leaders of six major civil rights organisations - including the NAACP, which advocated a legal strategy, and SCLC, agreed to stage a mass demonstration in Washington.
Afraid that violence would derail their cause, they recruited 4,000 volunteers to keep order.
The choice of venue - in front of the Lincoln Memorial - was hardly accidental.
President Abraham Lincoln had freed the slaves, and previously black singer Marian Anderson had sung from its steps - at the behest of First Lady Eleanor Roosevelt - when she had been denied admission to Washington concert halls.
But the size of the turnout - and its inter-racial nature - exceeded all expectations.
Among the speakers were white trade union leader Walter Reuther and white religious leaders like Rabbi Joachim Prinz.
Thousands listened in the afternoon sunshine to the famous words of Dr King's "I have a dream" speech:
"When we let freedom ring, when we let it ring from every tenement and every hamlet, from every state and every city, we will be able to speed up that day when all of God's children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands and sing in the words of the old Negro spiritual, Free at last, free at last. Thank God Almighty, we are free at last."
Violence and division
But the sense of progress felt that summer by the civil rights movement was soon to be challenged.
Less than a month later, four black schoolgirls were killed by a bomb placed in a Birmingham church by a white supremacist.
And in three months, President Kennedy was dead, assassinated in Dallas, Texas.
His successor, Lyndon Johnson, a white southerner, eventually proved the best friend the civil rights movement ever had.
But it took many more months of struggle - a struggle which increasingly involved whites as well as blacks in the "Freedom Summer" of 1964 - before major civil rights legislation was agreed.
It took many months of struggle after the march before legislation was agreed
And it was not until 1965 - and another summer of confrontation at Selma, Alabama - that the Voting Rights Act gave political power to southern blacks.
Splits in the movement
By then unity that had characterised the early civil rights movement had also come under severe strain.
Some of the students who had united behind Dr King developed their own organisation - the Student Non-Violent Coordinating Committee (SNCC) - into a vehicle for black power which opposed Dr King's approach.
White trade unionists became alienated from the black civil rights movement over demands for local community control of schools and teacher hiring, especially in a bitter strike in New York City.
And starting in 1966, a series of riots convulsed northern cities like Los Angeles, Newark, and Detroit, as black people expressed frustration over the slow pace of change in the North.
Eventually, Dr King himself turned North to engage in the struggle for economic justice and opposition to the war in Vietnam before being assassinated in 1968.
By that time, the civil rights movement had transformed the political and social landscape of America for good.
Forty years after the March on Washington, in June this year, the US Supreme Court upheld one of its key achievements - the idea of affirmative action to increase the representation of minority students at elite universities.