Columbia subject headings:
Harvard subject headings:
Postcards--Europe--History--20th century--Congresses.
World War, 1914-1918--Art and the war--Congresses.
World War, 1914-1918--Pictorial works--Congresses.
Princeton subject headings:
Postcards--Europe--History--20th century--Congresses.
World War, 1914-1918--Art and the war--Congresses.
World War, 1914-1918--Pictorial works--Congresses.