Washington, D.C. native and legendary bandmaster John Philip Sousa (1854-1932) wrote a dozen operettas, six full-length operas, and over 100 marches, earning the title “March King”.  He enlisted in the United States Marine Corps at an early age and went on to become the conductor of the President’s Own United States Marine Band at age 26.  In 1892 he formed “Sousa and his Band”, which toured the United States and the world under his directorship for the next forty years to great acclaim.  Not only was Sousa’s band hugely popular, but it also exposed audiences all over the world to the latest, cutting-edge music, bringing excerpts of Wagner’s Parsifal to New York a decade before the Metropolitan Opera staged it, and introducing ragtime to Europe, helping to spark many a composer’s interest in American music.

About El Capitan (1896), from Paul E. Bierley‘s The Works of John Philip Sousa:

One of the perennial Sousa favorites, this march has enjoyed exceptional popularity with bands since it first appeared. It was extracted from the most successful of the Sousa operettas, El Capitan. El Capitan of the operetta was the comical and cowardly Don Medigua, the early seventeenth-century viceroy of Peru. Some of the themes appear in more than one act, and the closing theme of the march is the same rousing theme which ends the operetta. 

This was the march played by the Sousa Band, augmented to over a hundred men and all at Sousa’s personal expense, as they led Admiral Dewey’s victory parade in New York on September 30, 1899. It was a matter of sentiment with Sousa, because the same march had been played by the band on Dewey’s warship Olympia as it sailed out of Mirs Bay on the way to attack Manila during the Spanish-American War.

El Capitan is one of the very few Sousa marches that begins in 6/8 and ends in 2/4, a distinction which it owes to its origins in the material from the operetta. See more about El Capitan at the US Marine Band Complete Marches of John Philip Sousa site (parts and score are free there), Wikipedia (about the operetta), The Guide to Light Opera and Operetta (again about the operetta), and IMSLP.

Here is a definitive US Marine Band performance, complete with a score preview:

Here is a short excerpt of the operetta in concert performance: