People like to say that history repeats itself, but Ken Burns isn’t buying it.

“Every event is new and unique,” documentarian Burns says. “What doesn’t change is human nature. Human nature stays the same. Mark Twain is supposed to have said, ‘History doesn’t repeat itself, but it rhymes.’”

Burns’ latest mammoth documentary series, “The Vietnam War,” which he co-directed with Lynn Novick, rhymes a little too well with present-day America. The 10-part, 18-hour film — aired on PBS in 2017 and eligible for several Emmy categories including doc or nonfiction series — takes an in-depth look into one of the most divisive and controversial events in American history: A period in time when the nation was polarized, women were struggling for equality, African-Americans were fighting to end discrimination and many citizens had little faith in the government.

The parallels between now and America 50 years ago are not lost on Burns or Novick, but when the pair began working on the project back in 2007, President Trump, the #MeToo and the Black Lives Matter movements didn’t exist.

“When we decided to make the film 11 years ago we could not have imagined what our world would look like right now, but we definitely had the sense of how fractured our society was back then in 2007,” Novick says. “How polarized and how the lack of civil discourse had become such a big problem. We saw a lot of the problems that we saw around us back in the Vietnam War era, and that was part of the reason for wanting to make the film.”

The directors initially anticipated a 14-hour, seven-part series complete with archival footage, never-before-heard audio and interviews with American soldiers, politicians and protesters. But after collecting interviews with Vietnamese war participants, the film’s runtime increased.

“We wanted to make sure that we represented the Vietnam War as not only an American experience,” Novick says. “We wanted to make a film true to as many Vietnamese perspectives as we could, but we initially had no idea how those stories would play out. Ultimately, the depth of richness of the Vietnamese stories affected the scope of the film.”

While the docu may sound lengthy, making “Vietnam” fit into an 18-hour time frame meant plenty of cutting. The directors conducted 100 interviews, which led to several hundred hours of footage. They also had to contend with thousands of hours of archival footage.

“The final year or two for us was a very long and tenuous editing process,” Burns says. “The cutting-room floor was just littered with not bad stuff, but really, really good stuff that unfortunately didn’t fit. So it was in some ways exhilarating and in other ways hell to edit this film.”

Burns notes that as with his other series, “The Vietnam War” resonates with the present-day, but the way the film rhymes with today’s current events is startling.

“When I was promoting ‘Vietnam,’ I would stand up and say, ‘What if I told you I made a film about mass demonstrations all across the country against the president. About a White House in disarray, obsessed with leaks. About a president certain that the press is lying and making up stories. About big document drops of stolen classified material. Well, the film I made is not about the present moment. It’s about Vietnam.’”

While the similarities between both time periods are alarming, Novick and Burns remain hopeful about the future. “I’ve spoken with people who didn’t live through the era and when they see ‘Vietnam’ they realize, ‘Wow! Our country has been through some pretty terrible times and we found a way to get through it,’” says Novick. “I find that that’s reassuring in a paradoxical way.”

And while Burns calls the Trump presidency “the greatest existential threat we’ve had to the United States since maybe the Civil War,” he remains optimistic. “I think that despite the fact that human nature doesn’t change, history is a rising road.”