'Show Boat' (1927)
Based on a novel of the same name, "Show Boat" was the first production where songs were written to fit the story, as opposed to just being added in. Set in late-19th century Mississippi, the play was produced by Oscar Hammerstein (who wrote the book and music) and Jerome Kern.
"What Oscar clearly did," said Broadway composer Stephen Sondheim in an NPR interview, "was to take operetta principles and wed them to American musical comedy, say, song and dialogue intermixed that would tell a story and tell a story of some emotional truth and reality."
Although "Show Boat" featured a beautiful score, as well as stunning choreography and sets, the musical took on dark and grown-up subject matters, like alcoholism, gambling and race. In fact, it was one of the very first musicals to have an integrated cast [source: Lunden].
Possibly best-known for the breakout song, "Old Man River," it is at its core a tale of love and unconditional friendship of performers aboard the riverboat "Cotton Blossom." One of the central characters, Julie, is kicked off the boat when it is discovered that she is of mixed-race (she narrowly avoids being arrested for the affront of her existence). Although bad habits take a major toll on the characters, they also experience redemption and forgiveness.