Columbia subject headings:
Harvard subject headings:
Europe--Emigration and immigration--Economic aspects.
Europe--Emigration and immigration--History--20th century.
Europeans--United States--History--20th century.
Immigrants--United States--History--20th century
Shipping--Atlantic Ocean--Economic aspects.
Shipping--Atlantic Ocean--History--20th century.
Shipping--Economic aspects--Atlantic Ocean.
United States--Emigration and immigration--Economic aspects.
United States--Emigration and immigration--History--20th century.
Princeton subject headings:
Europe--Emigration and immigration--Economic aspects.
Europe--Emigration and immigration--History--20th century.
Europeans--America--History--20th century.
Immigrants--America--History--20th century.