Columbia subject headings:
Harvard subject headings:
Labor movement--History--20th century.
Peace-building--Congresses--History.
Socialism--History
War and socialism--Europe--History.
War and socialism--Switzerland--History.
World War, 1914-1918--Peace
Zimmerwald Conference (1915)
Zimmerwald movement
Princeton subject headings:
Labor movement--History--20th century.
Peace-building--Congresses--History.
Socialism--History.
War and socialism--Europe--History.
War and socialism--Switzerland--History.
World War, 1914-1918--Peace.
Zimmerwald Conference (1915)
Zimmerwald movement.