Columbia subject headings:
Harvard subject headings:
Labor unions--Europe--History
Labor unions--United States--History
Social classes--Europe--History
Social classes--United States--History
Working class--Europe--History
Working class--United States--History
Princeton subject headings:
Labor unions--Europe--History.
Labor unions--United States--History.
Social classes--Europe--History.
Social classes--United States--History.
Working class--Europe--History.
Working class--United States--History.