There had been musicals before. In the 1930s, as soon as sound permitted, Warner Brothers developed what we call the Busby Berkeley pictures: they were black and white, and often aware of the harsh Depression times, but a choreographic lather of girls and fluid, orgasmic forms where the camera was itching to plunge into the centre of the "big O" – think of Footlight Parade, Gold Diggers of 1933 or 42nd Street. They had aerial shots of waves and whirlpools of chorus girls, opening and closing their legs in time with our desire. A few years later, at RKO Pictures, the Astaire-Rogers films came into being – where the gravity, beauty, and exhilaration of the set-piece numbers (effectively directed by Astaire) ignored the weightless framework of the stories and their inane romantic complications.
Great article and two vids embedded as well including SInging in the Rain.
How I love all these wonderful musical!