Sousa wrote The Gallant Seventh in 1922 in the midst of his career conducting the smash-hit Sousa Band.  It was his most popular march of the 1920s.  According to naxosdirect.com:

The Seventh Regiment of the New York National Guard for years had one of the famous bands in the New York City area. Their conductor, Francis Sutherland had been one of Sousa’s cornettists. The premiere of the march was performed on the stage of New York’s great Hippodrome Theater (predecessor of today’s Radio City Music Hall) with Sousa’s Band flanked by Sutherland’s Seventh Regiment Band.

Read the New York Times account of this premiere performance (also Sousa’s 68th birthday celebration) here.

The Gallant Seventh program notes.

This is fantastic: someone made a flash game using The Gallant Seventh!  Don’t be fooled by the super-fast tempo in the game.

Sousa shrine – including biography, complete works, and much more – at the Dallas Wind Symphony website.

John Philip Sousa on Wikipedia

Finally, a youtube performance the US Marine Band: