Columbia subject headings:
Forced labor--History--Congresses.
Slave labor--History--Congresses.
Slavery--Economic aspects--Congresses.
Slavery--History--Congresses.
Slavery--Social aspects--Congresses.
Harvard subject headings:
Forced labor--History--Congresses.
Slave labor--History--Congresses.
Slavery--Economic aspects--Congresses.
Slavery--History--Congresses.
Slavery--Social aspects--Congresses.
Princeton subject headings:
Forced labor--History--Congresses.
Slave labor--History--Congresses.
Slavery--Economic aspects--Congresses.
Slavery--History--Congresses.
Slavery--Social aspects--Congresses.