Columbia subject headings:
Slavery--United States.
United States--Economic conditions.
United States--Politics and government--1849-1861.
Harvard subject headings:
Slave labor
Slavery--Economic aspects--United States
Slavery--United States--Controversial literature.
United States--Politics and government--1849-1861.
Princeton subject headings:
Slave labor.
Slavery--Economic aspects--United States.
Slavery--United States--Controversial literature.
United States--Politics and government--1849-1861.