Columbia subject headings:
Chad--Commerce--Libya--History--20th century.
Chad--History.
Libya--Commerce--Chad--History--20th century.
Sahara--Commerce--History--20th century.
Senussites--History--20th century.
Harvard subject headings:
Chad--Commerce--Libya--History--20th century.
Chad--History
Libya--Commerce--Chad--History--20th century.
Sahara--Commerce--History--20th century.
Senussites--History--20th century.
Princeton subject headings:
Chad--History--19th century.
Chad--Relations--France.
Chad--Relations--Libya.
France--Relations--Chad.
Libya--Relations--Chad.