Lil Nas X did Ken Burns a favor.

For eight years, the documentary filmmaker known for tackling not-small subjects such as The Civil War (1990), Jazz (2001), and The Vietnam War (2017) has been toiling on another epic. The eight-part, 16-hour-plus documentary miniseries, Country Music: A Film by Ken Burns, begins airing on WHYY12 in Philadelphia and PBS stations nationally on Sept. 15.

Country Music poses an essential question: What is country music? That’s essentially the same one brought about by the success of “Old Town Road,” Lil Nas X’s enormous “Is it country, or is it rap?” hit that has caused country music gatekeepers to wring their hands in 2019.

The miniseries has an almost accidental relevance due to Lil Nas’ popularity, although the documentary shows that the debate has always been raging.

To Burns’ credit, his exhaustive — and yes, when taken in big gulps, kind of exhausting — history goes out of its way to portray country as non-monolithic, not exclusively white, music that from its beginnings has been a mongrel mix drawn from various sources.

In the fourth installment, which covers the 1950s rise of Patsy Cline, the Memphis rockabilly of Elvis Presley and Johnny Cash, and Ray Charles’ soul-country foray across the racial divide, Burns’ go-to narrator Peter Coyote intones that “country music had always been a mixture of influences from its diverse, entangled roots, including Appalachian ballads, gospel, cowboy songs, and the blues.”

The miniseries covers 75 years of country, starting in 1923, when visionary record man Ralph Peer recorded Fiddlin’ John Carson singing “The Little Old Log Cabin in the Lane” and ending in 1996, when Garth Brooks was at the height of his stadium-sized popularity. The persistent, patient show makes time for the many strands of the country story, interlaced with 20th century societal upheaval and technological change.

There’s the jazzy Western Swing of Bob Wills & the Texas Playboys, bluegrass of Bill Monroe, soul-searing honky-tonk of Hank Williams, down-home genius of Loretta Lynn and Dolly Parton, country rock of the Byrds, Outlaw rebellion of Willie Nelson and Waylon Jennings, and the New Traditionalist uprising of Steve Earle and Dwight Yoakam.

As Vince Gill puts it: “If you asked what country music is, it wouldn’t be one thing. It’s been a million things.”

Burns emphasizes the ways country has woven together the musical styles, songs, and instrumentation of rural whites and blacks.

He highlights the contributions of African Americans like mainstream successes Charley Pride and Darius Rucker, while shining light on racism as in the case of DeFord Bailey, the original Grand Ole Opry harmonica player fired in 1941 because he was labeled “lazy.”

A.P. Carter, the patriarch of the foundational band the Carter Family — who recorded classics like “Wildwood Flower” and “Keep on the Sunnyside” across the river from Philadelphia at the Victor Recording Company in Camden — built the group’s repertoire by traveling in the rural South with his African American “songcatcher” associate, blues man Lesley Riddle.

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There are many examples of white country stars who went onto fame after studying under the tutelage of lesser-known black musicians. “Hillbilly Shakespeare” Hank Williams was mentored by African American street musician Rufus “Tee Tot” Payne. And country’s cross-cultural combinations go all the way back: Banjos come from Africa, fiddles from the British Isles.

Burns brings that history into play to inform a debate that’s always under discussion in a musical genre that has nostalgia for bygone days deep in its DNA. Whenever the forces of modernity threaten to strip away its core values, the old ways are romanticized and valorized.

The documentary — which can be accompanied by a five-CD, 105-song box set whose music is also available in condensed form on a 58-song Spotify playlist — arrives as a spirited debate is already under way.

That’s thanks to Lil Nas, the cowboy hat-wearing 20-year-old rapper from Georgia whose song earlier this year exposed racial bias at country radio stations. It was excluded from Billboard’s country chart because “it does not embrace enough elements of today’s country music,” even though its twangy sound is more “country” than most (often hip-hop flavored) bro-country pablum.

Lil Nas got the last laugh, of course, with the song ruling the Billboard pop chart for a record 19 consecutive weeks. And in righteous rebel tradition, he appears to be already opening doors and changing the idea of what country is: “The Git Up,” a dance track by African American country rapper Blanco Brown, has gone where “Old Town Road” never did and topped the country charts.

Burns has explained his decision to end Country Music in the 1990s because, as he told The Boot this spring, “we’re in the history business.” “History is about the perspective that the passage of time permits you to have. As you get closer to the present, you suddenly realize you’re kind of on thin ice about making decisions.”

That offers Burns an easy way out — he didn’t want to make the hard decisions — when it comes to assessing recent developments in country, as the massively popular business has gotten further and further away from the musical touchstones treated with such reverence in the documentary, to the point that most new music that sounds truly country is labeled alt-country or Americana.

But Country Music does serve a relevant role in providing historical context and background to the current debate about country’s identity, even if it doesn’t speak to that issue directly.

It’s also compelling edutainment, as the director uses his trademark “Ken Burns effect” of zooming in and panning over old still photographs to provide a sense of action when no video footage is available.

Burns employs a who’s who of talking heads, lots of whom are impassioned and informed, like Rosanne Cash, Rhiannon Giddens, Ketch Secor of Old Crow Medicine Show, and Marty Stuart. These are people who care a lot, and know a lot. Stuart is particularly fab, with mandolin in hand, ready to demonstrate the (tiny) differences between Earl Scruggs‘ “Foggy Mountain Breakdown” and Bill Monroe’s “Bluegrass Breakdown.”

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Country Music is a little heartbreaking, with screen time with now-deceased giants like Merle Haggard and Ralph Stanley. (We miss you, Hag!) But there are living legends on hand, too, such as Parton and Tom. T. Hall.

Brenda Lee is a particularly winning presence, remembering being looked after when she was a 12-year-old sensation by Cline, whom she calls “a great broad,” and breaking into an impromptu version of Williams’ “I’m So Lonesome I Could Cry.”

Country Music is as authoritative and well researched as you would expect, but can be frustrating in what it chooses to leave out, sometimes opting for the safe and obvious over the risky.

Bob Wills is rightly given his due — with jazz explication from Wynton Marsalis and anecdotes by Asleep at the Wheel leader and Springfield, Montgomery County, native Ray Benson. But how do you not include Spade Cooley, the Los Angeles World War II era Western Swing king who was convicted of the murder of his wife?

Similarly, the big names of the Sun Records rockabilly explosion are included. But lovable weirdos like Charlie Feathers are left by the wayside. Fans seeking more insight into country’s dank and dark underbelly are recommended to check out Tyler Mahan Coe’s Cocaine & Rhinestones podcast.

The documentary is subtitled “A History of America, One Song at a Time.” And Burns is armed with bushel baskets full of great songs, from Jimmie Rodgers’ “T.B. Blues” to Kitty Wells’ “It Wasn’t God who Made Honky Tonk Angels” to Randy Travis’ “Diggin’ Up Bones.”

Country Music does a laudable job of using those songs to frame the history of a music that’s a mélange of sounds and traditions brought to the U.S. from elsewhere that and then forged in economically disadvantaged communities into something long lasting and true. “Three chords & the truth,” in an enduring adage.

The resulting cultural achievement is “probably the white man’s soul music” in the words of Kris Kristofferson. It’s not the least of Burns’ accomplishments to show that it wasn’t shaped only by white men and women, and demonstrate that it still has the ability to speak to the souls of us all.

Ken Burns’ Country Music will be previewed Tuesday, Sept. 10 at the World Cafe Live, with a performance by Langhorne Slim and discussion between WHYY-FM (90.9) host Marty Moss-Coane, WXPN-FM (88.5) deejay Dan Reed and author Tara Murtha.