Today, the 1957 musical “West Side Story” makes its return to Broadway in a radically reconceived new production by director Ivo van Hove. It’s a show that millions of people have seen onstage and screen and think they know: the white Jets finger-snapping down the street to take on the Puerto Rican Sharks, their rival gang; the score by Leonard Bernstein and Stephen Sondheim that has become part of the American songbook with standards like “Tonight,” “America” and “I Feel Pretty.” And who can forget Jerome Robbins’s iconic choreography?

Yet most fans of the show don’t know that the familiar “West Side Story” was not the show that the creators originally had in mind. Initially called “East Side Story,” the show was going to be about Jews and Catholics fighting in the streets of New York’s Lower East Side during the holidays of Passover and Easter. This original concept was more than a fleeting idea; it underwent multiple drafts in 1954 and 1955. So how did the musical go from “East” to “West,” and why didn’t “East Side Story” ever come to light? The answer lies in the show’s complex racial politics. “West Side Story” is about more than gang battles between white and Latinx New Yorkers. Its history shows that it is really a glimpse into the always changing, always moving boundaries around race and ethnicity in America.

“West Side Story” had its genesis when Robbins’s actor friend and lover, Montgomery Clift, who was performing the role of Romeo in Shakespeare’s “Romeo and Juliet,” asked Robbins for advice on how he should approach his character. A lightbulb went on, dim at first: Make “Romeo and Juliet” contemporary.

The idea sat in Robbins’s head until 1949, when he called Bernstein and book writer Arthur Laurents. According to Bernstein, Robbins’s idea “was an East Side version of ‘Romeo and Juliet,’ involving as the feuding parties Catholics and Jews during the Passover-Easter season with tensions in the streets running high and a certain amount of slugging and bloodletting. ”

Instead of a family feud, it would feature a religion-oriented dispute, set in New York’s Lower East Side, “specifically, Allen Street for Juliet and the Capulets, Mulberry Street for Romeo and the Montagues,” according to Laurents in “West Side Story’s” 1957 Playbill.

Romeo would be Italian, while Laurents envisioned the Capulets as Jewish. His script took its cue directly from the Bard. The play opened with a fight involving Mercutio, Benvolio and Romeo. Romeo had been following Rosaline, much as in Shakespeare’s original. But his friends teased him: “He ought to know better than to ‘chase a Jew babe.’ ‘They don’t put out.’ But ‘Rosalind ain’t orthodox’ etc.”

Laurents didn’t amend Shakespeare’s story much, except for the ethnic and religious backgrounds of the characters. Laurents wrote that “the difference in religion should not matter to either of them,” and he envisioned Juliet explaining “she is a cousin come to visit the Capulets for the Passover holidays with her Tante.”

An early script, in fact, featured a Passover Seder at the Capulets, with a mention of the Four Questions. Tybalt, the child who should ask the questions, is absent because he is “loafing with that gang,” or so thinks his “irritated” mother. But the audience learns that Romeo has actually murdered Tybalt, and police are chasing him as the Seder progressed.

A show featuring Jewish cultural traditions like the specifics of a Seder would have been revolutionary at the time. Broadway’s most Jewish musical, “Fiddler on the Roof” (1964), was still a few years away. Putting Jewishness onstage so overtly would have been game-changing.

But two crucial issues forced “East Side Story’s” reworking: First it was too similar to “Abie’s Irish Rose,” the 1922 Broadway play by Anne Nichols about an Irish woman and Jewish man who fall in love, which ran for 2,327 performances. Even more important was that the proposed show’s racial politics were already fiercely dated. Jews and Catholics might have had some latent animosity, but they were hardly murdering each other on the streets of the East Side in the late 1940s and early 1950s. There had been an influx of Latin Americans, and the Jewish-Catholic ghettos were no longer “the exclusive zones of gang rivalry.”

More broadly, in the years after World War II, the racial and ethnic landscape of the United States, particularly the country’s white landscape, was quickly changing. Once-maligned ethnic minorities, including Jews, Irish and Italians were becoming part of a new white mainstream that had been previously reserved only for WASPs, while people of color (particularly African Americans and Hispanic Americans) now found themselves on the rungs of the racial ladder once occupied by these white ethnics. This reality would have left “East Side Story” appearing dated and out of touch.

In 1955, the pieces to what would become “West Side Story” finally fell into place. During a casual poolside conversation, Bernstein and Laurents spied a headline in a Los Angeles newspaper, “More Mayhem from Chicano Gangs,” prompting them to muse about using Latin music in the show, and the musical began to come together in their heads.

Laurents, though, had no knowledge of Chicanos in Los Angeles. As he wrote in his memoirs: “New York and Harlem I knew firsthand, and Puerto Ricans and Negroes and immigrants who had become Americans.” But he saw the potential and knew that the new direction meant the show wouldn’t be “Abie’s Irish Rose.” “It would have Latin passion, immigrant anger, shared resentment. The potential was there, this could well be a ‘Romeo’ to excite all of us.” Bernstein and Laurents quickly called Robbins, who agreed with this new direction for the show.

That thunderbolt led to “West Side Story,” which became one of the most popular musicals of all time.

Its roots, like those of the show’s creators themselves, were definitively Jewish, reflecting a time when racial categories in the United States were changing and white ethnics, such as Jews, could achieve new success in society, in part by demonizing people of color. “West Side Story,” therefore, is not just a musical about rival gangs on the streets of New York, it’s a window into the racial politics of the United States in the mid-20th century.

Van Hove’s new production not only radically reimagines the show with new choreography, video elements and internal cuts. It continues this evolution of changing racial lines. This production, which has been partially contemporized — the Jets are no longer all white, but a variety of races, while the Sharks are still Latinx — represents less a racial divide than a divide that currently roils America over immigration and the building of walls: native-born vs. foreign-born individuals.

In this way, van Hove knowingly or not signals that “West Side Story” has always been about the ways that race and identity are constantly changing and reformulating themselves in America. The show’s original creators grappled with this concept as they were devising their 1950s opus and eschewed religious tensions for racial ones. Just as the original 1957 production was meant to be a window into the racial politics of the day, so too does this new “West Side Story” speak to contemporary audiences, highlighting the ways in which race, ethnicity and identity, while always changing, are also ever present in the experiment that is America.