Columbia subject headings:
Harvard subject headings:
Emigration and immigration--History--Congresses.
Foreign workers--History--Congresses.
Labor movement--Historiography--Congresses.
Labor movement--History--Congresses.
Migrant labor--History--Congresses.
Popular fronts--History--Congresses.
Princeton subject headings:
Foreign workers--Congresses.
Working class--Congresses.