How did Pyotr Ilyich Tchaikovsky transform ballet into a staged musical drama?

Pyotr Ilyich Tchaikovsky transformed ballet from a primarily decorative gesture into a sophisticated staged musical drama by elevating it to the level of symphonic music.1

He achieved this revolution through several key innovations:

• Symphonic Design: Tchaikovsky applied a symphonist’s sense of large-scale structure to his ballet scores. Unlike his predecessors, who often used random or purely decorative layouts, he organized successive dances using specific keys to create a cumulative sense of purpose and narrative momentum.1
• Melodic Integration: He possessed a unique ability to let melody engender the dance, ensuring that the music was not merely a rhythmic servant to the dancers but an equal partner in the performance.12
• Integrity of Composition: By bringing an integrity of design to his works, he ensured that his ballets possessed a "soul," moving beyond the superficiality that characterized much of the 19th-century ballet repertoire.12

Through these techniques, Tchaikovsky established a new standard for the genre, influencing later composers such as Sergey Prokofiev and Aram Khachaturian.1