There’s a not-so-subtle divide in the Kings of Leon’s musical output, which stretches 15 years and seven albums. If the first two releases are chock-full of piss and vinegar — a homespun hybrid of the Strokes and the soulful classic rock of their southern brethren, complete with requisite tight pants, big beards and moral depravity — the five that followed share an altogether less acidic tone.

In the wake of a 2006 tour with U2, a new batch of songs emerged, offering a more spacious sound with a decidedly pop sheen. Two years later, on the back of singles “Sex on Fire” and “Use Somebody,” Kings of Leon were one of the biggest rock bands in the world.

While recording its latest album, WALLS, the group — comprised of three brothers and their cousin — hoped to recapture a bit of that early days fire while retaining the winning alchemy of the latter releases. As frontman Caleb Followill puts it, to “rekindle that love that we had in the beginning.” The resulting album is Kings of Leon's most focused and joyous since its breakthrough. It also happens to be their first American number 1.

READ: Kings of Leon reveal the story behind 'Reverend'

“The style of [early album] writing, we could probably tap into really easily. But we weren't trying to have a certain kind of sound or write super simple parts because it was cool, it's just all that we could do,” bassist Jared Followill says of the band's musical evolution. “It's like a basketball player who has horrible form but still makes threes, and he becomes a better and better player but they're like, 'Man, I wish he would shoot it like he used to.' It's hard to go back to something once you've moved past it.”

“I don't feel like it would be a hard thing to do,” Caleb interjects, contradicting his younger brother. “I'm still playing the same guitar from the same amp. Obviously getting back to singing like that I'd have to force it a little bit because back then I was trying to mask what I was saying. I was afraid that people wouldn't like my lyrics, so I was singing them muffled. I could do that again. I mean, if that's what the people wanted, I could do that.”

Below, the Followill brothers recall the five songs that changed their lives.

'Wicker Chair' (2013)

Caleb: It was the first song I ever wrote on a guitar so that song is special to me.

'Milk' (2004)

Caleb: The first real collaboration. That was Jared's guitar part and I just started singing over the top of it. That was the first time that we did something together.

'Sex on Fire' (2008)

Caleb: "Sex on Fire" changed our lives a little bit. I could not afford [expensive] sweaters before that song, I promise.

'On Call' (2007)

Jared: Because of the Times was a paradigm shift in our band. We had toured with U2 and Pearl Jam and saw you could play these bigger places and write these songs that were more popular and still keep your integrity and still be cool.

'Trani' (2003)

Caleb: That was a big one for me because we always try to tell stories in our songs and that was one of the best stories we ever told, I thought. I feel like I couldn't write that song right now, it would be too risqué to call a song that but back then nobody really cared. So it was kind of a special thing we got away with. Mr. Bob Dylan said that was a hell of a song.