Explain why Ziegfeild took a risk opening Showboat in his new theatre and why it was groundbreaking for African American theatre?

A few weeks later, under the new title of ''Oklahoma!,'' Rodgers and ... play'' arrived in New York and changed the course of American musical theater ... into a moody, bittersweet libretto that took little time out for the formulaic, ... both the serious Broadway musical and of Sondheim's groundbreaking career.