The document outlines significant figures and contributions in 20th-century music, categorizing it into genres such as jazz, musicals, and rock & roll. Key individuals mentioned include John Philip Sousa, Gustav Holst, Igor Stravinsky, and Duke Ellington, alongside important works like 'The Planets' and 'Rhapsody in Blue.' It also highlights Broadway's evolution and landmark musicals like 'West Side Story' and 'The Lion King.'