How did Johann Strauss II use waltzes in Die Fledermaus?

In Die Fledermaus (1874), Johann Strauss II integrated waltzes as a fundamental element of the work's high-spirited musical character. Rather than serving merely as incidental dance music, these waltz themes are woven into the operetta's structure to enhance its lighthearted and festive atmosphere.1

The most prominent use of the genre occurs during the grand party scene in Act II, where Strauss employs waltz themes to drive the revelry and romantic tension of the narrative. Specifically, the act concludes with a rousing finale titled "Im Feuerstrom der Reben," where the characters toast to champagne and dance, effectively using the waltz to sustain the momentum of the scene as the plot reaches its climax.1

By incorporating these dance forms—alongside polkas—Strauss leveraged his reputation as the "Waltz King" to define the classical example of Viennese operetta. His ability to blend these rhythmic, melodic dance pieces with the dramatic requirements of the stage helped ensure the work's enduring popularity and musical success.213