TheatreHistory.com
Theatre History: American Musical Theatre: An Introduction
A commercial website that provides a solid history of American musical theatre. Includes summaries of many musicals through history. Focus is on shows before 1960.
Musicals 101
Musicals101: History of the Stage Musical 1910 1920
From Jerome Kern's Americanized shows to the Ziegfeld Follies, the stages saw a whole new type of musical from 1910-1920.