Columbia subject headings:
Middle class--Europe--History--19th century--Congresses.
Social classes--Europe--History--19th century--Congresses.
Working class--Europe--History--19th century--Congresses.
Harvard subject headings:
Middle class--Europe--History--19th century--Congresses.
Social classes--Europe--History--19th century--Congresses.
Working class--Europe--History--19th century--Congresses.
Princeton subject headings:
Middle class--Europe--History--19th century.
Working class--Europe--History--19th century.