OH, WHAT a beautiful mornin’ it was for the American musical theatre in the 1940s and 1950s. The previous era of great songs gave way to the new era of great shows in the heady atmosphere of a life-and-death struggle of a world war and the subsequent euphoria of peace. Somehow the old “music and girls” format was no longer enough.

Richard Rodgers and Oscar Hammerstein II’s Oklahoma! (1943) ushered in musicals with stories that made dramatic sense and numbers that helped to tell them: Brigadoon, On the Town, Lady in the Dark, Annie Get Your Gun, Kiss Me, Kate ...

As the careers of Betty Comden and Adolph Green show, talent crossed back and forth from Broadway to the movies. By the Fifties there was a complete synchronicity of tone and musicals were at the centre of popular culture.

Hollywood poured money into Technicolor screen versions of Broadway greats, even spending eight months in Nogales, Arizona, to make it look like Oklahoma. After almost five years on Broadway, the movie version of South Pacific became the highest-grossing film of 1958, with its soundtrack staying in the charts for 262 weeks and making it the bestselling LP of the second half of the Fifties.

The groundbreaking Broadway show West Side Story — a perfect synthesis of drama, music and dance — was only a moderate stage success (audiences preferred the down-homey Americana of The Music Man). But the 1961 film version scooped ten Oscars and the soundtrack album was No 1 in the Billboard charts for a staggering 54 weeks. What America was watching and listening to were one and the same.

Yet West Side Story was looking back to Broadway’s Golden Age while also looking forward to the cult of youth (where are the parents in its story of battling gangs?). By the Sixties, with the mainstream giving way to the maverick and guitars replacing keyboards and the pop of the past, the Great American Songbook largely written by Broadway and Hollywood’s finest was replaced by rock.

In turn the TV variety shows that had traditionally hosted selections from Broadway musicals began to disappear. Worse, radio no longer gave old-fashioned-sounding musicals serious airplay, so album sales plummeted.

Rock had arrived, building up a back catalogue that Ben Elton would later plunder for shows of shoehorned hits. That old lullaby of Broadway would never be the same again.