Columbia subject headings:
Working class--Europe.
Working class--Latin America.
Working class--North America.
Harvard subject headings:
Working class--Europe--History--Chronology.
Working class--History--Chronology.
Working class--Latin America--History--Chronology.
Working class--North America--History--Chronology.
Princeton subject headings:
Working class--Europe--History--Chronology.
Working class--History--Chronology.
Working class--Latin America--History--Chronology.
Working class--North America--History--Chronology.