At the time, Carson’s pioneering late night variety show had become one of the country’s most influential platforms. So the move to have Belafonte take this mainstream institution and transform it into a multicultural and political experience, introducing white America to his world of art and activism, was unprecedented.

Belafonte became the first Black person to host a late-night TV show — even if it was only for a week, as Richard Nixon’s problematic and controversial presidency loomed ominously on the horizon. His guests also included notable African Americans of the day like Lena Horne, Nipsey Russell, Bill Cosby, and others, all engaged in searing, in-depth interviews, taking place in an America that was forced to really contend with itself as a country on the verge of radical change. The Civil Rights and Voting Rights Acts, for example, which still left Black Americans behind economically, signaled some progress, no matter how incremental.

Each guest came across as thoughtful and admirable — but also shaken by the uncertainty of the time. It was clear and understandable that none of them had answers to the country’s complications. But the show wasn’t all politics. As host, Belafonte also entertained his audience with comedy and music. Watching Paul Newman play the trombone, reliving his role as an expatriate trombonist in Martin Ritt’s 1961 drama “Paris Blues,” which co-starred Sidney Poitier and Joanne Woodward, was especially a treat. The charming Belafonte also verbally jousted with announcer Ed McMahon, and showed home videos of his family on vacation. Other guests included singers Buffy Sainte-Marie, Petula Clark, Dionne Warwick, and Robert Goulet; comedians Tom and Dick Smothers; actor Sidney Poitier; poet laureate Marianne Moore; and others, mostly African American. A ratings success, Belafonte’s week-long “Tonight Show” hosting engagement offered a very necessary panoramic view of an America that was on the cusp of transformative social change, featuring celebrity guest interviews — even though edged with gloom — were collectively working to close gaps between the races and classes. “The Sit-In” captures the importance of this lost broadcast history. Now, 93-year-old Belafonte — a staunch supporter of progressives like Bernie Sanders, who served as honorary co-chair for the 2017 Women’s March on Washington — has devoted his twilight years to social activism, outliving many of the guests he hosted on “The Tonight Show” during that February week in 1968; people he called friends who were working to create an environment that wouldn’t tolerate the killings of Trayvon Martin in 2013, or Freddie Gray in 2015, and George Floyd most recently.

The documentary highlights never-before-seen footage from this pivotal time, which set the stage for the confluence of late-night and politics that audiences appreciate today. A must-watch, “The Sit-In: Harry Belafonte Hosts The Tonight Show” premieres September 10, on NBCUniversal’s streaming platform Peacock. Sign Up: Stay on top of the latest breaking film and TV news! Sign up for our Email Newsletters here.