Gerald Segal
Simon and Schuster, 1996
Buku Referensi
D.C. The World Bank , 1994
Buku Teks
De Blij, Harm J.
John Wiley & Sons, 1993
Buku Teks
Penna, Anthony N
Blackwell, 2013
Buku Teks
edited by John Parham, Louise Westling
Cambridge University Press, 2017
Buku Teks