Bone, Hugh A., author
McGraw-Hill, 1965
Buku Teks
Ranney, Austin, author
Harcourt, Brace and Company, 1956
Buku Teks
Greenstein, Fred I., author
Englewood Cliffs, 1970
Buku Teks
Huntington, Samuel P., author
The Belknap Press, 1981
Buku Teks
Jupp, James
London Melbourne University Press 1964
Buku Teks