Hough, Jerry F.
The Brookings Institution, 1980
Buku Teks
Frederick A, Praeger; George Allen and Unwin Ltd., 1964
Buku Teks
edited by Alexander Dalllin, Gail W. Lapidus
Westview press, 1991
Buku Teks
Dallin, David
Hollis & Carter, 1949
Buku Teks
McCauley, Martin
Longman, 1993
Buku Teks