In the 1990s, Chicago filmmaker Denis Mueller produced several documentaries that focused on the darker moments in American history–films like The FBI’s War on Black America, John Edgar Hoover and the Great American Inquisitions, and Citizen Soldier: The Story of the Vietnam Veterans Against the War. By 1997, Mueller says, he was looking to make a film about the nature of history itself–“how it relates to society and how it’s approached with different points of view.”

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Then one day he happened upon Failure to Quit: Reflections of an Optimistic Historian, a 1993 collection of essays and speeches by Howard Zinn, the retired Boston University professor who’s spent much of his own career challenging official versions of historical truth. “I knew who he was–I’d read A People’s History of the United States years ago, but I’d forgotten about it,” says Mueller, now a PhD candidate in American studies at Bowling Green State University. Inspired, he picked up Zinn’s 1994 autobiography, You Can’t Be Neutral on a Moving Train: A Personal History of Our Times. “I thought, he’s had a fascinating life–why don’t we do something on this guy?”

The filmmakers couldn’t have anticipated how true this statement would prove. After September 11, Zinn, then 79, reemerged as a leading critic of U.S. military and foreign policy. As a public speaker, he was suddenly more in demand than ever. “It really changed things–the war on terrorism gave the documentary a third act,” says Mueller. “We knew we would have an audience, but we never knew how timely the film would become–that he would become popular again and reach a whole new generation of young people.”