Columbia subject headings:
Canal Zone--Foreign public opinion--History--20th century.
Panama--Foreign relations--United States--Public opinion.
Public opinion--United States--History--20th century.
United States--Foreign relations--Panama--Public opinion.
Harvard subject headings:
Canal Zone--Foreign public opinion--History--20th century.
Panama--Foreign relations--United States--Public opinion.
Public opinion--United States--History--20th century
United States--Foreign relations--Panama--Public opinion.
Princeton subject headings:
Canal Zone--History.
Panama Canal (Panama)--History.