Questions and Topics We Can Help You Answering; 

Please read this part carefully!
Choose a particular dimension of the musical, for example “leading lady,” harmony, scenes v. individual songs, form, opening numbers, act 1 finales, dream sequences, sexualities, a particular performer, or specific character types.  How has the dimension you chose been treated throughout the history of the Broadway musical?  Include paragraph-length considerations of at least five shows from three different decades to support your assertions.  One show must be from before 1930.  (The Musical of the Month blog at New York Public Library is a great resource for information on many pre-1930 shows.  See http://www.nypl.org/voices/blogs/blog-channels/musical-of-the-month ) The essay has to follow with correct citations.  Your examples do not need to be limited to English-language musicals.
Show Boat would be a great example of this for your pre-1930 example.  Sondheim’s Follies and Assassins are two more examples of this.