Complex sentence: The Royal Theatre, first opened in 1922 as the black-owned Douglass Theatre, was the most famous theatre along West Baltimore City's Pennsylvania Avenue that was one of a circuit of five such theaters for black entertainment in big cities.
Split into simpler sentences: The Royal Theatre, first opened in 1922 as the black-owned Douglass Theatre, was the most famous theatre along West Baltimore City's Pennsylvania Avenue. It became one on a circuit of five theaters for black entertainment in big cities.