Columbia subject headings:
Emigration and immigration law--United States--History.
Labor supply--United States--History.
United States--Emigration and immigration--History.
Harvard subject headings:
Emigration and immigration law--United States--History.
Labor supply--United States--History.
United States--Emigration and immigration--History.
Princeton subject headings:
Emigration and immigration law--United States--History.
Labor supply--United States--History.
United States--Emigration and immigration--History.