When Ken Burns conducts an interview from his New Hampshire home, there's almost always a U.S. flag in the background. That's appropriate. TV's greatest history professor has churned out countless hours celebrating our country's can-do spirit in hits like "Jazz," "The Mayo Clinic" and "The National Parks." He's a patriot.

But the 70-year-old filmmaker isn't afraid to also direct projects that reveal our nation's ugly side. "The American Buffalo" is one of those.

The four-hour documentary, airing at 7 p.m. Monday and Tuesday on PBS, examines the swift downfall of the bison, an animal made nearly extinct by hunters, soldiers and other pioneers who got greedy.

"It is an unmitigated tragedy," Burns said last month during a Zoom conference with TV critics. "The first episode is, at time, incredibly difficult to watch when you see a species that numbered perhaps as many as 50 to 60 million — we had no way of knowing — dwindle down over the course of the 19th century to under a thousand, and most of them were in zoos or private herds and not running wild."

Narrator Peter Coyote guides us through a shameful tale of how the destruction of the mighty animal was intrinsically tied to a campaign to hurt Native Americans. Wiping out one of their main sources of sustenance was key to weakening their power.

Julianna Brannum, a citizen of the Comanche Nation of Oklahoma who served as a consulting producer on the project, said just looking into a bison's eye can be a spiritual experience for her people.

We talk about blood memory," she said during the news conference. "It's very emotional for me and it brings me to tears sometimes."

Part One focuses on the role of industrialists, who wanted roaming ranges for railroads, and opportunists like William Cody (voiced by Jeff Daniels) who got the nickname Buffalo Bill from his high number of kills. Dayton Duncan, the film's primary writer, says folks like that turned the Great Plains into a "factory floor." It would end up being the destructive period of wildlife in world history.

But stick around for Tuesday's conclusion. That's when the film shifts gears, focusing on efforts to make up for past mistakes by passing legislation and establishing zoos. It worked, to a degree. But intentions weren't always honorable. Was Cody trying to make up for past sins with his wildly popular traveling show that celebrated bison? Or was he just looking to make a fast buck?

Burns is at this best when examining the complicated nature of man.

"Achilles had his hubris and his heel to complement his great strength. I've yet to run into anybody who's perfect," he said. "All of our characters are 'a priori,' deeply flawed. And so then our narratives become that much more complicated but, I think, that much more interesting."

Viewers intimated by the weighty questions should be at least somewhat appeased by footage of buffalo running free in Montana, Texas, Oklahoma and South Dakota over the past two years. Those shots are like mugs of herbal tea after chugging rot-gut whiskey.

But Burns keeps returning to his role as history professor, one who's not about to let even the most patriotic American off the hook.

"We're now in a debate about censoring history. That doesn't work at all," he said. "If we are exceptional, then we need to be incredibly self-critical at every moment and to dive deep into stories, perhaps even more into the stories that are uncomfortable than in the comforting bromides that often pass for American history."