Columbia subject headings:
Drama--20th century--History and criticism--Congresses.
Drama--Political aspects--Congresses.
Theater--Political aspects--Congresses.
Harvard subject headings:
Drama--20th century--History and criticism--Congresses.
Theater--History--20th century--Congresses.
Princeton subject headings:
Drama--20th century--History and criticism--Congresses.
Theater--History--20th century--Congresses.