Berman, Harold J., author
Little, Brown, 1953
Buku Teks
Hough, Jerry F.
The Brookings Institution, 1980
Buku Teks
Frederick A, Praeger; George Allen and Unwin Ltd., 1964
Buku Teks
Gregory, James S., author
Penguin Books, 1946
Buku Teks
edited by Alexander Dalllin, Gail W. Lapidus
Westview press, 1991
Buku Teks