Columbia subject headings:
Slavery--United States--History--19th century.
United States--History--Civil War, 1861-1865--Causes.
Harvard subject headings:
Slavery--United States--History--19th century
United States--History--Civil War, 1861-1865--Causes
Princeton subject headings:
Slavery--United States--History--19th century.
United States--History--Civil War, 1861-1865--Causes.