This piece is the first in a series, continuing next week, about Ken Burns, the legacy of “The Civil War,” and race and politics in America.

“The Civil War” is a landmark of American documentary film. Forty million people watched the nine-part series when it first aired on PBS in 1990, and their enthusiasm helped spark a Civil War craze. “The Civil War” itself became a big business: videocassette sales set records for PBS and millions purchased a spin-off book. The film also made a star of Ken Burns, who had previously directed smaller movies about Huey Long, the Brooklyn Bridge and the Statue of Liberty.

Burns would go on to further establish himself as the country’s premier documentarian with epic examinations of American staples such as baseball and jazz, but 25 years later “The Civil War” is still the project he calls “my baby.”

In May, he and restoration artist Daniel J. White were holed up in a New York City editing facility to take a look at parts of a remastered — and in some ways very different — version of this American classic. The new edition of “The Civil War” will air on PBS starting Monday night, entering a conversation about race and American history that makes a quarter-century-old film about a 150-year-old war newly and sharply relevant. And as much as “The Civil War” changed Ken Burns’s life, the remastering process has given Burns the opportunity to really make the film he dreamed of more than 25 years ago.

“The Civil War” was remastered once before, in 2002, when it was released in digital format. But for this edition, Burns’s team at Florentine Films went back to the raw source material. Fifty thousand feet of film — the cheapest available at the time because it was all Burns and his partners could afford — had to be run through a machine called an ARRISCAN at a rate of one or two seconds per frame. The result was footage that hadn’t been degraded by repeated copying and that wasn’t contaminated by dust and other impurities.

The technical improvements to the film, including a new resolution that restores parts of images that were cropped away for the original TV broadcast, may be most interesting to hard-core film fans. But even casual viewers will be able to see that the remastered version of “The Civil War” is a strikingly different film from the movie that preceded it.

Burns and White used some variant of the word “murk” nine times in two hours of conversation to talk about what they were excited to eliminate from “The Civil War.” The result is a much clearer, and in some cases more nuanced, movie.

The lurid, iconic battlefield sunsets of the previous film now appear on screen streaked with blue, and while the landscapes retain what Burns calls a “painterly” quality, they look much more like actual places.

“I think what happened to the old landscapes was that because of the dullness of the reproduction and the copying, they then did something that worked against what we wanted. Now I think they’re doing what we want them to do,” Burns said of shots such as those of the sunsets or of Burnside’s Bridge, which became a choke point during the Battle of Antietam in 1862. “They’re doors and they’re mirrors. . . . There is the Burnside Bridge. I’d seen it in old archives. This is a real thing and here it is still there, and so it connects you to the past.”

Burns had to shoot historical photographs and documents with close-up attachments, degrading the image quality; in the remastered version of “The Civil War,” those shots gain details both large and small. The new images “essentially strip away what the 16 millimeter saw and get back to what I held in my hand, and to hold it at that degree of sharpness, and to say it’s really real,” Burns said, marveling at the clarity of the images that flashed across the editing room’s screen.

It’s now possible to read President Abraham Lincoln and Gen. George McClellan’s facial expressions in a snapshot of the two men taken during a meeting shortly before Lincoln fired his top commander.

“You can now see in the pictures of them in the tent the tension between them,” Burns said. “Now, it may have been apparent in the previous images because of the quality of the writing, whatever the music and the sound effects were suggesting, but now you’ve taken away that veil and you’re permitted to see that interpersonal dynamic, and suddenly you can understand McClellan’s kind of combination of arrogant distance from Lincoln and Lincoln’s exasperation, and the fact that his sorry butt is going to be axed in a couple of moments is terrific.”

Burns even pointed to one of the signature moments of the original film, the presentation of Sullivan Ballou’s love letter to his wife, Sarah, which closes out the first episode of the series, as a place where he’d seen improvement. “You saw we consciously chose [a picture] where the woman’s in focus and the man is not,” to illustrate the sequence. “But now, it’s conscious. It doesn’t look like, ‘Why did they pick a bad image?'”

For all White wanted to avoid changing the essential thrust of “The Civil War,” these changes have a cumulative effect on what it means to watch the film. Among the things the remaster makes more visceral are the many images of dead men and animals and the utter destruction of cities such as Richmond. Filtering through images in the editing room, a remastered shot of what turned out to be a dead horse especially stood out.

“It kind of concerned me,” White said, noting that the images of violence were starker in the remastered version, which had never shied away from the tally of the war in the first place. “You can see the dead men on the battlefield and you can see details in it now. It was kind of murky before. But now it is much more stark.”

If White was concerned, Burns was not.

“Our film, as crude as that original broadcast was, was revealing the real cost of war, albeit fought 150 years ago, but nonetheless the real cost of the war in which Americans killed other Americans, in which there were consequences for human bodies and consequences for American landscapes,” he said, reflecting on what it had been like to air “The Civil War” for the first time in the middle of the Gulf War. “And I think what this does is even make it sharper and more apparent. And that’s good because if you make a film about war, not one of your intentions but one of the byproducts ought to be how horrible war is. . . . I think the restoration helps that cost be experienced that much more directly and that much more effectively.”

Among all these other things, the remastered version of “The Civil War” is an act of preservation. Early in the final episode of the movie, Burns recounted what happened to Mathew Brady’s photographs of the conflict after Brady went bankrupt and his negatives were lost, given away or even sold for use in greenhouse construction.

“The sun sometimes burned the image of war from these countless old, glass-plate negatives, and it was to the real detriment of our memory of it,” Burns recalled. Now that his raw footage has been scanned for posterity, it will be saved from a similar fate. “In some ways, the film allows us to preserve this stuff, and to give it to a wide audience, and now to restore it and save it forever.”

Correction: An earlier version of this piece misstated the circumstances of George McClellan’s firing. We regret the error.