Here is a comprehensive summary of the Wikipedia article on "The Stars and Stripes Forever":

"The Stars and Stripes Forever" is a beloved American patriotic march composed by John Philip Sousa in 1896, and it was officially designated as the National March of the United States by an act of Congress in 1987. Sousa composed the piece on Christmas Day while aboard the ship Teutonic, after learning of the death of his band manager, David Blakely, and it premiered to great enthusiasm in Philadelphia on May 14, 1897. In the entertainment world, the tune was famously used as a "disaster march"—a subtle code to alert theater and circus staff of life-threatening emergencies without causing panic, as notably seen during the tragic Hartford circus fire of 1944. Musically, it follows the standard military march form with repeated strains, culminating in the famous "Grandioso" trio featuring a piccolo obligato and trombone countermelody, which Sousa intended to symbolize the North, South, and West uniting as the Union. Written for a full concert band, the piece also includes Sousa's own lyrics, though they are far less known than its iconic instrumental melody.