On Sept. 26, 1957, Broadway changed forever when the curtain went up on “West Side Story.”

The artistic innovations popped immediately: Instead of an overture, the orchestra played Leonard Bernstein’s jagged musical phrases, punctuated by actors snapping their fingers. Rather than stock musical-theater characters, the story foregrounded rival gang members wearing dirty blue jeans who lurked on street corners. Actors danced throughout the show not just for aesthetic effect, but to express themselves, a new storytelling approach by director and choreographer Jerome Robbins. And in what was unheard of for a musical at the time, the show ended not with a send-em-home-happy finale, but with a heartbreaking death.

As “West Side Story” celebrates its 60th anniversary, it stands as more than art: It was an artistic confrontation of social issues from immigration and bigotry to economic inequality and gang violence.

But it didn’t quite start out that way.

Initially, Robbins had envisioned “East Side Story,” an update to Shakespeare’s “Romeo and Juliet” set as a clash between Catholics and Jews in Manhattan’s Lower East Side.

When playwright Arthur Laurents joined the creative team, he saw the set-up as tired. “He worried that ‘East Side Story’ would settle into a musical version of the 1922 play ‘Abie’s Irish Rose,’ a schmaltzy interfaith romantic comedy about Irish Catholics and Jews by Anne Nichols,” wrote Misha Berson, author of Something’s Coming, Something Good, a history of “West Side Story.”

A new idea came in 1955 when Laurents and Bernstein were coincidentally both staying at the Beverly Hills Hotel in Los Angeles. While lounging at the pool, they saw a newspaper headline about Chicano youth gang violence, and the immediacy of the issue set them on a discussion. Why not shift their concept to Puerto Ricans, a new ethnic group flooding into New York? (Puerto Rican immigration to the U.S. peaked in the 1950s at nearly half a million, more than all who came in the entire first half of the century.)

Robbins loved the idea. But work on the project would come in fits and starts as all the creative team members were pulled onto major projects. When Bernstein realized he didn’t have time to write the libretto, the search for a lyricist led to a young Stephen Sondheim.

He accepted the job with some concern. Berson recounts that he expressed his hesitancy to his agent by saying: “I’ve never been poor and I’ve never even known a Puerto Rican.”

Robbins himself had to do some research. He went to the Puerto Rican section of Harlem to watch a high school dance and made detailed notes on dances he had never seen before, according to Robbins biographer Deborah Jowitt.

When rehearsals began, Robbins wanted the cast, which had no established stars, to really feel like turf-defending street toughs and their girls. He instructed them to follow Method acting, a technique in which performers adopt their characters’ emotional and psychological states.

To enhance the us-versus-them mood, Robbins forbade socializing between actors who were playing the Jets, the white gang, and the Sharks, the Puerto Ricans.

“Read this; this is your life,” he wrote and posted on a bulletin board along with a newspaper article about a gang killing.

For Broadway veteran Chita Rivera, whose portrayal of Anita became the breakout role of her career, that article hit home. “It was very poignant. It had just happened the night before, and it was two blocks away from our rehearsal studio, [at] a playground that we passed all the time,” she told HISTORY. “I realized that this was our life, and this [story] is possible because it happened. We were looking straight at it and we carried the fear, that urgency with us.”

Musically, Bernstein was busy creating a Latin-accented score so full of complexity and percussion that even today’s dancers find it fiendishly difficult to stay in sync with the counts.

“When it came to it being so Latin, Broadway had never heard music like this in the theater,” says Rivera. “It takes practice if you don’t hear this music in your ear, in your soul and in your house when you are a kid.”

The best example of the score’s richness comes in the song “Maria” and its use of a “tritone,” a succession of notes that goes up by three whole adjacent tones—nicknamed “the Devil’s interval” in musical circles because its unresolved progression often sounds sinister or unsettling. Bernstein’s score as a whole was so difficult that when Columbia Records executives initially considered a Broadway cast recording, they wanted to pass based on the dense lyrics and depressing story.

The story raised more than one objection. While the Puerto Rican characters are fully developed, they are based on negative stereotypes of violence and poverty. That duality has not diminished over time: As “Hamilton” creator Lin-Manuel Miranda said before the 2009 bilingual Broadway revival, for which he wrote translations, “West Side Story” has been the Latino community’s “greatest blessing and our greatest curse.”

Part of the blessing lies the opportunity to showcase Latino and Latina stars, though that wasn’t quite the case in the 1961 film. George Chakiris, an actor of Greek descent, was cast as Bernardo, Maria’s brother, and wore obvious streaks of brown facial makeup in the film.

The show’s explicit depiction of racial division scared off some Broadway investors, according to Berson: “And it also kept away some show goers with uninformed, preconceived negative opinions of Puerto Ricans.”

Broadway may not have been ready for “West Side Story.” Despite its critical success, it had a modest run of 732 performances and won only two Tony Awards, for choreography and set design. The award for best musical that season went to “The Music Man,” a far more conventional show.

But American culture was catching up: The 1961 film, which follow the stage play closely, won 10 Academy Awards, including best picture.

“The show was ahead of its time, and the movie was in the cross hairs of the zeitgeist,” says theater professor Laurence Maslon of New York University’s Tisch School of the Arts and editor of American Musicals (1927-1969).

Without the film, it’s an open question how widely the material would have been known.

But as it is, more than 45,000 productions have happened all over the world—with some interesting, and politicized, regional variations. One production, mounted in Leipzig, East Germany at the end of the Cold War, reflected a particularly negative image of American culture—one where gang warfare was common, says Thomas Albert, producing artistic director of the Shenandoah Summer Music Theatre. Albert says a former teaching colleague who saw the production in person describes its final moments as far bleaker than the Broadway version. Instead of the hopeful image of the two gangs joining together to carry away Tony’s lifeless body, the East German version ended with the gangs exiting separately, leaving the corpse alone on stage. This was underscored musically by the emphatic dissonance of the final measure’s unresolved tritone, something Bernstein himself had tweaked in the Broadway staging to be less unsettling—offering if not a “musical ray of hope,” says Albert, at least “an uneasy truce.”

The show has left a massive legacy. Its music has fueled jazz interpretations for decades. Its real-world drama, fully merged with dance, pioneered the genre of youth musicals such as “Rent” and “Hair” and encouraged new forms of storytelling that are still evolving on the Broadway stage today. And its 400-year-old story, retold for the 1950s, has found a lasting place in the hearts of millions.

Pia Catton is editor-in-chief of Dance.com. Follow her on Twitter and Instagram at @piacatton.