Final answer:
Sousa's contributions to march music enhanced its suitability for military precision, collective unity, and national pride, reflecting the spirit of American progress and patriotism.
Step-by-step explanation:
Sousa's innovations in the march made the form more conducive to military precision, collective unity, and the display of national pride. These changes reflect a shift towards ensemble performance and the importance of the music in fostering a sense of collective identity and shared purpose. Sousa's music was sophisticated yet accessible, perfect for both concert performance and actual marching, and it embodied the spirit of American progress and patriotism, supporting military and civic events.