Bangtan Sonyeondan — better known to western audiences as BTS — made a record-setting splash on the Billboard charts last month. With a No. 1 album on the Billboard 200 and a top-10 single to boot, the band’s success marks a new chapter in the history of Asian music in America, a chapter radically distinct from previous novelty acts such as “Gangnam Style” phenom Psy.

Not even a high roller would have gambled on its success. When K-pop first tried to breach the American music market, it used the success of Shakira as its model. Early attempts such as BoA’s “Eat You Up” and Girls’ Generation’s “The Boys” aimed for radio success and strained to appeal to a wide audience through English lyrics and hook-laden songwriting.

BTS threw out that rulebook. The band members do not sing in English, aside from a phrase here and there. The band’s music cannot be defined as a crossover hit: the band barely has radio play, its Spotify streaming numbers are tepid, and your average American probably couldn’t name a single member, much less a song.

Instead, what BTS managed to pull off is even more impressive — it gathered a devoted fan base without the help of traditional American musical institutions, a fan base that is a large enough that the band no longer needs to appeal to the general public.

Pop musicians who can carry albums without hit singles to lure in the masses are a rarity — think Madonna, Beyoncé or Lorde — but not since M.I.A’s Maya has a pop act tried this hard to spurn success and stuck to its niche. BTS’ latest, Love Yourself 轉 ‘Tear,’ the last of a triptych of albums, is not what we would expect for its triumphant American breakthrough.

There is an established way to create music that crosses the language barrier — examples include Las Ketchup’s “Aserejé” and Daddy Yankee’s “Gasolina” — and Tear does not follow it.

Previous globetrotting K-pop hits, such as Girls’ Generation’s “Gee,” have choruses as distinct from their verses as cannon fire is from water gun squirts. In “Gee,” the vocals goose-step in time with the militant 4/4 of the bass. This is the perfect translinguistic hit, carefully constructed so that the theme — being suddenly struck by love — is apparent without the rather disposable lyrics.

This is the tradition that the Bangtan Boys, as the bandmates are sometimes called, are working against. There are four singers and three rappers — an unusually high number of the latter for a K-pop group. The Bangtan Boys’ song lengths are long for pop music, clocking in usually at about four minutes. Their choruses tend to come a full minute into the song. Their verses tend to be rap-heavy and, since each rapper has his own flow, are distinct from one another. This is not ideal pop music composition; this is not your momma’s radio-friendly K-pop.

The album is a return to the R&B and hip-hop sounds of the group’s 2014 record Dark & Wild, after a couple of years on an EDM-flavored detour. A strong R&B vibe in K-pop is unusual.

The linchpins of an R&B sound — a muffled transition from the verses to a chorus, slippery vocals that stray from the beat — work against catchiness, that cornerstone of pop music success.

In short, the band’s compositions tend to be loose, formless and, for K-pop songs, relatively hookless. BTS’ success, then, marks the maturity of K-pop listening tastes in America. No longer are Western K-pop fans charmed merely by just flashy music videos, perfectly coordinated dance sets and simple earworm tunes — they take K-pop seriously as an artistic medium and hunger for authenticity and experimentation within its confines.

What sets BTS apart from its boy band competitors is that it co-writes and sometimes co-produces its own material. If the tracks on Tear are somewhat clumsy in composition, so be it — it is merely a marker of the band’s self-made bona fides. On Tear, there are songs mourning the loneliness of Pluto and celebrating the life-changing magic of giving up — hardly typical boy band subjects. BTS’ fanbase aren’t just excited by the pretty boys — there are plenty of those in the K-pop scene already — but are genuinely excited by the unpredictableness of its music, its lyrics, its behavior.

The enormous success of BTS signals that K-pop has completed the transition from novelty to subculture to genre in America. This understates what is actually a major event in American musical history; there is now a big enough market in America for Korean pop music that bands such as BTS can bypass the mainstream entirely and still make good money.

Where is BTS then? It might be geographically Korean, but its fanbase really lives in the enormous undersea threads of the world wide web. BTS’ mysterious popularity in America, despite having little presence on the national stage, is because its fanbase has little to do with national boundaries. Its songs aren’t meant to dominate radio waves — they’re to win the adulation of BTS’ fans, to live on in Tweets and blogs, to become popular from the margins. These songs sneak up on the mainstream when it isn’t looking and take us all by surprise.

Contact Adesh Thapliyal at [email protected]. Tweet him at @AdeshThapliyal.