“The March” 10 p.m. Tuesday, OPB

It was organized in only a few weeks and lasted just 10 hours. The American president was only reluctantly on board with it and many among the public expected it to deteriorate into riots. But destiny was not to be denied on that hot August day: The 1963 March on Washington was, as the new PBS documentary “The March” rightly concludes, “the event that changed American politics forever.”

The film, airing Tuesday night,, lasts only an hour, but it easily proves its point about the lasting historical significance of the march, which drew between 200,000 and 300,000 people — black and white — for the March on Washington for Jobs and Freedom on Aug. 28, 1963.

It wasn’t just that there were that many people in attendance, or that Dr. Martin Luther King Jr. delivered the “I Have a Dream” speech for which he will be remembered for all time: It was that the march rescued the civil rights movement from losing its moment in history, as author Taylor Branch says, by fulfilling A. Philip Randolph’s call to make civil rights a truly national cause.

Of course, through the entire story, we are waiting for the grand finale, which can only be King’s speech. When it comes, you’ll be hard-pressed to withhold tears, not only because of the power of King’s words and his heroic cultural status, but because the filmmakers have carefully prepped us to understand just a little of the great struggle that led to those moments on the afternoon King spoke in front of the Lincoln Memorial.

The entire history of the African American struggle is far too complex and detailed to be contained in a single hour, much less in just part of one as a prelude to the march. The PBS film gives us greater perspective and insight, probing the conflicted attitudes toward civil rights in the Kennedy administration.

Of course, there is much more the documentary could have explored, such as how the march fits in one of the single most decisive years in American history, a year that saw the death of Medgar Evers, and, later on, the death of a president. In a brief afterword, the film includes footage of President Lyndon B. Johnson signing the 1964 Civil Rights Act, first proposed on June 11, 1963, by Kennedy as an anti-segregation bill.