Many birthday presents are rapidly discarded or forgotten, but a gift given to a 17-year-old Michigan high-school student, on 29 July 1970, changed American television. Ken Burns received an 8mm movie camera, the first step on a path that made him such a revered figure in documentary film-making that, five decades later, his birthday this year will be celebrated with a whole day of his work on the PBS network.

If 66 seems an odd birthday to be so honoured, it is because, on the more conventional landmark last year, Burns was locked away editing his latest eight-part, 16-hour series, Country Music, which airs in September. That work forms, with Baseball and Jazz, a loose trilogy about emblematically American sports and culture. Those series are a peacetime balance to another thematic trio: The Civil War, The War and The Vietnam War, grippingly authoritative revisitings of the conflicts in which America was engaged between 1861-65, 1941-45, and 1954-73.

What had Burns learned from selecting his retrospective? “While the stories I have told stretch from the 18th century to the 21st, all asked one deceptively simple question: who are we? That strange and very complicated people who like to call ourselves Americans. I’ve had the privilege to work for 45 years in the space between this two-letter plural pronoun ‘us’ and its capitalised equivalent in my country: the US. The opportunity not to tell just a traditional top-down story – Winston Churchill in the war room – but the bottom-up story of what it’s like to be on the battlefield or the street.”

‘Baseball was a sequel to The Civil War’ … Ken Burns. Photograph: UPI/Alamy

Although Burns had made earlier impact with cinema documentaries – Brooklyn Bridge and The Statue of Liberty were both Oscar-nominated – his defining work began in 1990 with a move into long-form television histories, for the nine-part The Civil War, charting the fight between north and south over slavery. For Burns, this was the only place to begin his grand project of historical self-analysis. “It was,” he says, “the greatest existential threat to the United States. We had been founded in 1776 on the assumption that all men are created equal. But – four score and five years later – four million Americans were owned by other Americans.”

Critics, with their cataloguing habits, have assumed that Burns set out to create a war trilogy. But the film-maker protests: “It really wasn’t. There’s been no agenda. I have been drawn to subjects completely emotionally: I’m finishing something up and my eye is drawn to something else. When The Civil War series was finished, it had been so emotionally wrenching to work on that story – even though we were at a remove of 150 years – that I vowed never to do another film on war. Then I realised that my next series, Baseball, was actually a sequel to The Civil War. Although people always look at me as if I’m crazy when I say that.”

Such looks are echoed in my bemused silence down a phone line to Burns’ office in New Hampshire. He explains, though, that “the first real progress with regard to race after the Civil War” came when, on 14 April 1947, Jackie Robinson walked out for the Brooklyn Dodgers as the first African American to play Major League Baseball.

Milestone moment … Jackie Robinson in Burns’s film Baseball. Photograph: NBL

Working on Baseball, Burns decided that the best musical soundtrack for that story was jazz: “And I realised that – though I had grown up listening to jazz, which my father enjoyed – I was woefully ignorant about what it was, and its racial significance. So, for me, Civil War, Baseball and Jazz are a sort of war trilogy.”

When Jazz was released in 2001, Burns was still expecting to stick to his pledge never formally to document another American conflict. “Then I learned that 1,000 Americans a day, veterans of the second world war, were dying, and I realised those memories were quickly going to disappear. I also discovered that many, many high-school students thought we fought with the Germans against the Russians. I was so stunned at that gross ignorance that I decided to do the world war two film. Then, even before we had finished that project, I had decided to do Vietnam, which took almost 11 years.”

The projects take so long because of the exhaustive collection of material – “For Country Music, I had 101 interviews, representing 175 hours of conversation, and 1,500 photographs” – and the perfectionist assemblage of the final film.

‘I was woefully ignorant about what it was’ … Burns’s documentary Jazz. King Oliver’s Creole Jazz Band Photograph: Frank Driggs Collection/PBS

“Many of my colleagues in this business,” says Burns, “will research for a certain period and then write a script, which informs the shooting and the editing. We never stop researching, never stop reading, looking for photographs, writing. Nothing is set in stone. I’ve got a neon sign, in cursive script, in my editing room that reads: It’s Complicated. Although most of the process of editing is by nature subtractive, often the last thing we do in the editing room is add something.”

Rewatching The Civil War after having seen The Vietnam War, I was struck, in retrospect, by how audacious Burns had been to make the earlier series with none of the elements – living witnesses, contemporary news footage – that helped to make the latter so impressive. Had he worried at the time about filling 11 and half hours of TV with a story from a pre-cinematic era? “Abraham Lincoln, faced with a whole string of second-rate, inferior generals, said, ‘We must use the tools we have.’ Each film has been an exercise in saying, ‘How do we do this?’ Sometimes, there can be a tyranny towards too much footage. Sometimes, in Vietnam and Baseball, we used still photographs, even though film was available.”

Audacious film-making … Union army general Ulysses S Grant in The Civil War. Photograph: CS Associates/PBS

Burns is nervous of formulas for film-making. “I see style as the authentic application of technique. And there are dozens of techniques that might be employed. Put simply, I have eight basic elements at my disposal: four visual, four aural. At any time, we have the possibility of – visually – interviews, or ‘talking heads’, live cinematography, still photographs, motion pictures. Aurally, we will have a third-person narrator; a chorus of third person voices, reading the journals or love letters of the period; a complex Hollywood-style sound-effects track; and music, which is recorded before the editing.”

Availability, though, should not mandate use. The first three images in Country Music, documenting a subject with a vast film and TV archive, are two still photos and a painting. Jazz and Country Music have another technical departure: “In documentary film-making, music is usually this important thing, but always in the background. So there is a beautiful shock in the music suddenly reaching this hyper-ground right in front of you. It happened to us several times while editing Jazz and Country Music.”

A measure of Burns’ meticulousness is his attitude to “lower thirds”, the captions at the bottom of a screen, identifying speakers. Burns gives the job that they held at the point in the narrative we have reached, so newspaper reporters who later became celebrated novelists are identified with the job title on their press card at the time. That’s presumably a way of avoiding hindsight and keeping in the present tense. “Absolutely. In the world war two series, we interviewed a woman who was a widow, but we used her maiden name because, at that point, she was the sister of brothers we were talking about. It’s only in the final episode of the film, when she gets married, that we use her married name.”

Bill Monroe on stage at the Grand Ole Opry, Nashville, c.1958. Photograph: Les Leverett Collection

In the first episode of Country Music, which charts the geographical spread of the form, even superstars are identified by where they come from (“Dolly Parton, Tennessee”), rather than who they are.

Yet, even for a producer as scrupulous as Burns, there is the challenge of living in an era when President Trump has pioneered the idea of “alternative facts”, and online posters increasingly regard history and news as a matter of opinion. Is that worrying for a maker of history documentaries? “Well, it’s certainly worrying as a citizen of the world, where we see not just the willingness of people to engage in dissembling, but the technological ability to do so. But a huge majority of your readers – and my viewers – are still interested in fact.

“In anticipation of what we thought would be our most controversial film, The Vietnam War, we assembled what we called our war room of Republicans and Democrats on different sides of the debate, who were skilled in putting out fires. We did not need to use them because we were so fiercely loyal to facts. If you do that, people trust you. We tried to show that there can be more than one truth in war.”

What it’s like to be on the battlefield … from Burns’s film about the second world war. Photograph: PBS

In an address to the graduating class at Stanford University in California in 2016, shortly before Trump became the Republican nominee, Burns warned that the reality-TV star had “a total lack of historical awareness, a political paranoia that, predictably, points fingers, always making the other wrong … The sense of commonwealth, of shared sacrifice, of trust, so much a part of American life, is eroding fast, spurred along and amplified by an amoral internet that permits a lie to circle the globe three times before the truth can get started.”

Three years on, Burns says: “Everything I said, I’m so very sorry to say, has come true.” But, as a historian, does he see the 45th president as an aberration or a continuation? “I think he is without precedent, which is what makes him so dangerous. And yet he is the embodiment of certain tendencies and attitudes that have been present throughout our history – anti-immigration, anti-black, sort of proto-fascist, dissembling, all of that. We’ve just never had it so glaringly in a chief executive. And it seems to be what’s in the drinking water of the Earth at the moment as you watch the ascension of Boris Johnson, the rise of dictators in Turkey and Hungary and the Philippines. There is a tendency to suggest that you can be expedient with the truth – and I don’t think you can.”

Burns’ accidental war trilogy is about to become an informal quartet, with a planned series about the American revolutionary wars of 1775-83. “I don’t want, as we tend to do in this country, to make it a superficial, sanitised event among a few dozen white men in Philadelphia, but to cover everything that was going on from New Hampshire to Georgia, the people who stayed loyal to Great Britain, African-Americans, British soldiers, American officers. And so, despite constantly never wanting to make another war film, I keep doing so because it is where human beings reveal themselves most prominently – for good or ill.”

• Ken Burns Day is on PBS on 29 July. Country Music is broadcast on PBS from 15 September.