Columbia subject headings:
Europe--Emigration and immigration--Social aspects--Congresses.
Immigrants--Europe--Congresses.
Political refugees--Europe--Congresses.
Harvard subject headings:
Europe--Emigration and immigration--19th century.
Europe--Emigration and immigration--20th century.
Political refugees--Europe--History--20th century.
Princeton subject headings:
Europe--Emigration and immigration--19th century.
Europe--Emigration and immigration--20th century.
Political refugees--Europe--History--20th century.