Quigley, Harold S., author
University of Minnesota Press, 1956
Buku Teks
McNelly, Theodore, author
Houghton Mifflin, 1972
Buku Teks
Pyle, Kenneth B.
AEI Press, 1992
Buku Teks
Ward, Robert E., author
Prentice-Hall, 1978
Buku Teks
Ward, Robert E., author
Prentice-Hall, 1967
Buku Teks