Three thousand country radio stations are beaming into America's heartland as you read this. The format has been growing steadily since the 1980s, and dwarfs all competition. Country is the deep mainstream of white America. Its recently retired king, Garth Brooks, has passed Elvis as the best-selling artist ever. But, outside America, most of country's modern stars might as well not exist. Brooks and his peers have been as inexplicable and un-exportable a phenomenon as George W Bush or Ronald Reagan.
Nineteen-year-old Taylor Swift's appearance at a country awards show last year playing acoustic guitar and hidden under a black hoodie looked like an affront to everything this conservative world stood for – till the top was torn off to reveal a respectable black dress. Signed to Brooks's Big Machine label in 2003, three years later she became the youngest ever singer and writer of a country No1 with "Our Song". She has ignored country's usual adult market, and written songs straight to teenagers. They have bought eight million of her records, and made her 2008's most searched for musician on MySpace.
In crucial ways, she is pure country. She grew up on a farm in Wyomissing, Pennsylvania (with a stockbroker dad), and writes honestly about her ordinary experiences, which, handily, are about dating boys. Mature dismissals of a "redneck heartbreaker" and the "pick-up truck you didn't let me drive" ("Picture to Burn") place her firmly in small-town, un-hip America.
The only problem you might detect is that she barely sounds country at all. Bar a vocal twang, and token fiddle, her ballads are the purest MTV pop. This 21st-century country strategy was pioneered by her acknowledged role models, Shania Twain and LeAnn Rimes. Twain's 2002 album Up! came with the same songs in country and non-country formats.
Swift is being determinedly launched across the Atlantic this month, alongside another country-pop act, Sugarland. The latter, duo Kristian Bush and Jennifer Nettles, are eight-million-selling double-Grammy-winners; Nettles sang at President Obama's inauguration, and has dueted with Adele, Bon Jovi, and Beyoncé.
But when I speak to Bush, they are having to begin their first European tour in US Air Force bases. A proper London gig next week, and a non-country mix of their single, "All I Want To Do", are intended as a bridgehead from Nashville to the unconquered UK. The pop gloss of third album Love On the Inside, with Nettles's Georgia twang and Bush's mandolin the only firm country signifiers, give them, like Swift, a fighting chance.
"In the last five or 10 years, country programmers have become a lot more liberal than you think," Bush explains of their hybrid sound. "People programming those stations now were music aficionados in the Eighties, and their playlists are wider. Country radio's essentially the home of the singer-songwriter now."
"The reach of country radio is so deep, it's got to the point where the fans are controlling the music," Bush believes. "When you have that many people, it becomes revolutionary – if they decide country music is X, Y or Z, because that's what they're gonna buy, the radio programmers and labels follow." These commercial imperatives mean country has its best chance yet of breaking into Britain. But even more than Swift, Sugarland suggest this is because everything that makes them country is being jettisoned, in a dive for the mainstream.
"Most days, I feel like I'm about to be vetted, and they'll find out I'm not real," Bush concedes. "I keep thinking: 'They're going to ask me a question about George Jones I don't know the answer to.' But those exclusive cultural identities don't exist the way they did. You can have a Sugarland sticker on your car next to Metallica, and nobody is offended."
More than any other music, country's whole history has been defined by this battle between commerce and authenticity. Its greatest artist, Hank Williams, wrote slick pop songs such as "Hey Good Lookin'", and bone-chilling laments straight from its Appalachian mountain roots. He died aged just 29 in 1953, a burnt-out proto-rock star. The very next year, Elvis Presley took country's rebellious tendencies for rock'n'roll. The country establishment, centring on Nashville's 16th Avenue (dubbed Music Row), reacted with the slick, string-sweetened "countrypolitan" style which dominated country in the 1960s.
"Nashville is Cashville," Time magazine declared in 1964, noting that, in the year of Beatlemania, the city's studios made 30 per cent of the nation's hits. Splashes of steel guitar and fiddle were deemed enough to suggest the music's rustic roots. The banjo in the video for Taylor Swift's "Picture to Burn" follows this precise formula.
There have been various insurgencies against this orthodoxy. In the 1970s, it was the outlaw country of Johnny Cash, Merle Haggard and Willie Nelson, and self-destructive Austin songwriters Guy Clark and Townes Van Zandt. The new country of the 1980s brought left-wing heroin addict Steve Earle, Dwight Yoakam, Lyle Lovett and kd lang. They all failed in Nashville. Their fresh energy instead led to Garth Brooks. His videos, showmanship, and overweight, balding, Everyman appeal nodded to country's roots with his Stetson.
Swift is on Brooks' label, and she and Sugarland live in the mainstream world he created. They'll most likely still be dismissed in Europe, as he was. Here, the deep-rooted country favoured by doomed rock musicians such as Gram Parsons in the 1960s is the only kind that counts with critics. Rugged, pill-popping Johnny Cash, whose ruined face at his end seemed carved from an older, truer world, is their icon. From Bob Dylan's country album Nashville Skyline (1969) to Jack White's production of Loretta Lynn's Van Lear Rose (2004), rock musicians queue to laud such veterans. Alt.country, the scene forged by Uncle Tupelo and the Jayhawks in the late 1980s, remains a hip rebuke to Music Row. Its current king, Will Oldham – aka Bonnie "Prince" Billy – has his latest album, Beware, out next week, too. His early records' vision of a stark, hellish, Appalachia chimed with critic Greil Marcus's influential notion of an "old, weird America", haunted by moonshine-swilling idiot-savants much like Oldham's stage persona. This is habitually viewed as a more real version of America than anything Nashville can produce.
But it may be that we're wrong. The baroquely bizarre rustic world beloved by Oldham and Marcus, and so readily believed in Britain, is fiction. Taylor Swift's high-school boyfriend troubles, Jennifer Nettles's wry resilience at divorce on Sugarland's second album Enjoy the Ride (2006), the Army-wife lament of the Dixie Chicks' hit "Travelin' Soldier" – these are the unrebellious, ordinary tales the tens of millions in country's actual audience, who really live in the suburban heartland it has always described, take comfort in hearing. There's a huge constituency just like it in Britain, in fact.
Bush can barely hide his impatience at alt.country's arrogance. "The songs that will survive 40 years from now will have to do, not with their excellence at how they interpreted post-modern Appalachia, but how they interpreted the human condition. And in the end, as much as I'm a huge Wilco fan, no one's going to remember them. They're going to remember Katy Perry's "I Kissed A Girl" – because that story is true. There'll be another girl sitting at a window who's kissed someone and that song speaks to her. And really, [Wilco and ex-Uncle Tupelo singer-songwriter] Jeff Tweedy singing about being lonely and poor and dumped, all these things which he is not...
"There are only so many thirtysomethings who'll emotionally connect to style over substance, which a lot of [modern] Appalachian stuff is. I'm a huge Gillian Welch fan, but she's from Malibu, California. I'm from Dolly Parton's hometown Sevierville, Tennessee. I should be playing what she's playing, according to our histories. Our song "Baby Girl" deals with some sort of human archetype, anyway, a story of the hero. It just rings differently in your bones. Country music is unafraid of that human substance."
Sugarland's 'Love On the Inside' is on Humphead Records. They tour the UK from March 16. 'Fearless' by Taylor Swift is out on Mercury this week. 'Beware' by Bonnie "Prince" Billy is out on Domino on Monday.