In another time, before the Internet left music splintered and compromised, First Aid Kit’s heart-grabbing “Emmylou” might have been an international hit.

A country-folk-pop duo from Sweden, First Aid Kit consists of sisters Johanna Söderberg, 24, and Klara, 21. “Emmylou” is a plea for love that won’t be extinguished, devotion of the kind that the June Carter-obsessed Johnny Cash sang about in the torch-song classic, “Ring of Fire.”

“I’ll be your Emmylou and I’ll be your June, ” the Söderbergs harmonize, “if you’ll be my Gram and my Johnny, too.”

In January, the Söderbergs released a golden-hued follow-up to “The Lion’s Roar,” the album that contains “Emmylou.” Like its predecessor, “Stay Gold” inspired heaps of praise from Billboard, Rolling Stone, Pitchfork and other publications.

First Aid Kit, following a sold-out U.K. tour that included the duo’s Royal Albert Hall debut, has returned to the U.S for a 21-city tour. This latest American visit includes a Thursday, Nov. 6, show at the House of Blues in New Orleans and the sisters’ debut at the church of country music, Nashville’s Ryman Auditorium.

For the Söderberg sisters, Royal Albert Hall was fun, scary and, from that day forward, unforgettable. They’re always thrilled about playing iconic venues, such as the Ryman, historic halls where they can almost feel the presence of those who went before.

The Söderbergs have played New Orleans twice before, as opening act for American band Bright Eyes and fellow Swede Lykke Li. Thursday’s show is their first headlining date in the city, a place with a culture that fascinates them and heat that oppresses them.

In 2007, when the sisters were still teens, Swedish radio aired their home-recorded song, “Tangerine.” They grew up with a musical father. As Klara recalled during a phone interview from Prague, “music has always been our passion, ever since we were kids. But then, when we started writing songs, we never thought, ‘OK, this is what we’re going to do now.’ We just loved writing songs.”

Early on, Klara and Johanna took the music of American artists the Carter Family, Gram Parsons, Leonard Cohen and Bob Dylan to heart.

“It was a revelation to us,” Johanna said. “It’s all authentic and real and raw. We could relate to it, because these are simple, regular human beings singing about their everyday lives. You don’t have to be a pop star or some kind of god to write interesting music that’s worth listening to.”

The possibility of having a career in music came quickly.

“But it was nothing planned at all,” Klara said. “We’re just really lucky.” And extremely talented. “But it takes more than that. There are so many talented musicians out there who don’t get recognized.”

In 2009, the U.K.-based Wichita Records released First Aid Kit’s first EP, “Drunken Trees.” A collaboration with American star Jack White followed. In White’s Nashville studio, they recorded their rendition of Buffy Sainte-Marie’s “Universal Soldier.”

The latest First Aid Kit news includes the group’s placement in the soundtrack of the new Reese Witherspoon movie, “Wild.” The Söderbergs’ rendition of R.E.M.’s “Walk Unafraid” is featured alongside songs by Bruce Springsteen, Simon and Garfunkel, Leonard Cohen, Wings, Portishead and Lucinda Williams.

“Walk Unafraid,” the sisters said, fits perfectly with the spiritual and physical journey Witherspoon’s character makes in “Wild.” Interpreting great songs by other artists is something the Söderbergs love to do anyway.

“We have so much fun singing covers in our free time,” Johanna said. “Singing is just automatic for us. We don’t have to think about it.”