'Serenade" was the first ballet George Balanchine choreographed in America, whereby he planted the seeds for the next 50 fertile years during which he reshaped classical ballet, with its French, Italian, Danish and Russian roots, as an American art form. It was 1934, he was 30 years old and just off the boat, literally, from St. Petersburg via Europe, where he had been Diaghilev's last choreographer for the Ballets Russes. He barely avoided detention at Ellis Island. "Serenade" was his third masterpiece (after "Apollon musagète" in 1928 and "Le Fils Prodigue" in 1929)—and the first of...