Madariaga, Salvador de
Frederick A. Praeger, 1958
Buku Teks
Adams, N. B.
Henry Holt, 1952
Buku Teks
Swanson, Earl H., author
Idaho State University, 1963
Buku Teks
Little, Brown & Co., 1998
Buku Teks
Rafael Altamira
Van Nostrand Reinhold Co., 1949
Buku Teks