Wilgus, A. Curtis
Barner & Noble, 1963
Buku Teks
Crawford, William R.
Frederick A. Praeger, 1961
Buku Teks
edited by Howard J. Wiarda, Harvey F. Kline
Westview Press, 2007
Buku Teks
Wynia, Gary W.
Cambridge University Press , 1984
Buku Teks
Susana Nuccetelli, Ofelia Schutte, Otavio Bueno
Wiley, 2013
Buku Teks