Columbia subject headings:
European Union countries--Emigration and immigration--Government policy.
United States--Emigration and immigration--Government policy.
Harvard subject headings:
Border security--Social aspects--European Union countries.
Border security--Social aspects--United States.
European Union countries--Emigration and immigration--Government policy.
United States--Emigration and immigration--Government policy.
Princeton subject headings:
European Union countries--Emigration and immigration--Government policy.
United States--Emigration and immigration--Government policy.