Ranney, Austin
Harcourt, Brace and Company, 1956
Buku Teks
Greenstein, Fred I.
Prentice-Hall, 1970
Buku Teks SO
Huntington, Samuel P.
The Belknap Press, 1981
Buku Teks
edited by Helen Jones and Susane Macgregor
Routledge, 1998
Buku Teks
Bone, Hugh A.
University of Washington Press, 1958
Buku Teks