Columbia subject headings:
Harvard subject headings:
Civilization, Modern--20th century--Congresses
History, Modern--20th century--Congresses.
Self--Social aspects--History--20th century--Congresses.
Princeton subject headings:
Civilization, Modern--20th century--Congresses.
History, Modern--20th century--Congresses.
Self--Social aspects--History--20th century--Congresses.