Columbia subject headings:
Harvard subject headings:
Forced labor--Europe--History--Congresses.
Forced labor--History--Congresses.
Foreign workers--Europe--History--Congresses.
Foreign workers--History--Congresses.
Labor market--Europe--History--Congresses.
Labor market--History--Congresses.
Princeton subject headings:
Emigration and immigration--History--Congresses.
Labor market--History--Congresses.