Why was Tchaikovsky important to the history of ballet music?

Pyotr Ilyich Tchaikovsky was a transformative figure in the history of ballet music because he elevated the genre from a merely decorative accompaniment to a sophisticated form of staged musical drama.1

Before Tchaikovsky, ballet music was often treated as a random or purely functional layout for dance. Tchaikovsky revolutionized this by applying a symphonist’s sense of large-scale structure, organizing successive dances through the use of keys to create a cumulative sense of purpose and integrity of design. By integrating his unique melodic gift with this symphonic rigor, he elevated ballet to the level of serious musical art.1

His influence is most clearly seen in his iconic scores for Swan Lake, The Sleeping Beauty, and The Nutcracker, the latter two of which were created in collaboration with the renowned choreographer Marius Petipa. Tchaikovsky’s experimental approach to melody and orchestration set a new standard for the genre, directly influencing later composers such as Sergey Prokofiev and Aram Khachaturian.231