Final answer:
The musical 'Oklahoma!' was the first to feature Agnes de Mille's revolutionary content-laden balletic choreography, with music written to complement the dance, unlike traditional musicals of the time. This bold move helped to set new storytelling standards in musical theatre.
Step-by-step explanation:
The musical that first dispensed with the decorative dancing girl chorus and featured content-laden balletic choreography by Agnes de Mille was Oklahoma! Agnes de Mille was revolutionary in insisting that the music be written to the choreography, rather than the other way around, which was the convention. Her choreography for the 18-minute-long dream ballet in Oklahoma! fully conveyed the emotional struggles and desires of the main character, Laurey, setting a new standard for storytelling in musical theatre.
This innovative approach was combined with the intelligent integration of successful elements from past productions by Rodgers and Hammerstein, such as social issues and dramatic dance sequences, to create a seamless production. The risk taken by the creative team by casting unknown actors, giving director Rouben Mamoulian complete control of the production, and starting the musical in an unconventional way contributed significantly to the success and popularity of Oklahoma!