Columbia subject headings:
Harvard subject headings:
Middle West--Description and travel.
Middle West--Economic conditions.
Middle West--Historical geography.
Northwestern States--Description and travel
Northwestern States--Economic conditions.
Northwestern States--Historical geography.
Princeton subject headings:
Middle West--Description and travel.
Middle West--Economic conditions.
Middle West--Historical geography.
Northwestern States--Description and travel.
Northwestern States--Economic conditions.
Northwestern States--Historical geography.