Columbia subject headings:
Agriculture--Economic aspects--America--History--20th century.
Agriculture--Economic aspects--Europe--History--20th century.
Agriculture--Economic aspects--History--20th century.
Harvard subject headings:
Agriculture--Economic aspects--America--History--20th century.
Agriculture--Economic aspects--Europe--History--20th century.
Agriculture--Economic aspects--History--20th century.
Princeton subject headings:
Agriculture--Economic aspects--America--History--20th century.
Agriculture--Economic aspects--Europe--History--20th century.
Agriculture--Economic aspects--History--20th century.