Columbia subject headings:
American newspapers--Ownership.
Canadian newspapers--Ownership.
Journalism--Economic aspects--Canada.
Journalism--Economic aspects--United States.
Press monopolies--Canada--History.
Press monopolies--United States--History.
Harvard subject headings:
American newspapers--Ownership
Canadian newspapers--Ownership
Journalism--Economic aspects--Canada.
Journalism--Economic aspects--United States.
Press monopolies--Canada--History.
Press monopolies--United States--History.
Princeton subject headings:
American newspapers--Ownership.
Canadian newspapers--Ownership.
Journalism--Economic aspects--Canada.
Journalism--Economic aspects--United States.
Press monopolies--Canada--History.
Press monopolies--United States--History.