Complex sentence: From 1954 to 1959, Mathias worked as the City Attorney of Frederick, where he supported civil rights for African Americans by desegregating the local opera house, which restricted black seating to the back of the theater.
Split into simpler sentences: From 1954 to 1959, Mathias worked as the City Attorney of Frederick, where he supported civil rights for African Americans. He played a role in desegregating the local opera house, which restricted African American seating to the back of the theater.