Columbia subject headings:
Emigration and immigration--History.
Equality.
Frontier and pioneer life--United States.
Labor supply.
Social classes.
Social history.
Harvard subject headings:
Emigration and immigration--History
Equality.
Frontier and pioneer life--United States
Labor supply.
Social classes.
Social history.
Princeton subject headings:
Emigration and immigration--History.
Equality.
Frontier and pioneer life--United States.
Labor supply.
Social classes.
Social history.