Columbia subject headings:
Industries--El Salvador--History.
Labor unions--El Salvador--History.
Working class--El Salvador--History.
Harvard subject headings:
Industries--El Salvador--History.
Labor unions--El Salvador--History.
Working class--El Salvador--History.
Princeton subject headings:
Industries--El Salvador--History.
Labor movement--El Salvador--History.
Labor unions--El Salvador--History.
Working class--El Salvador--History.