Columbia subject headings:
Socialism--Germany--History--Congresses.
Socialism--Scandinavia--History--Congresses.
Working class--Political activity--Germany--History--Congresses.
Working class--Political activity--Scandinavia--History--Congresses.
Harvard subject headings:
Labor unions--Europe, Central--Political activity--Congresses.
Labor unions--Scandinavia--Political activity--Congresses.
Princeton subject headings: