Hickok, Eugene W.
The Free Press, 1993
Buku Teks
Konrad Adenauer Stiftung (Yayasan Konrad Adenauer), 2004
Buku Teks
Huntington, Samuel P., author
The Belknap Press, 1981
Buku Teks
Roberts, Geoffrey
Manchester University Press, 1984
Buku Teks
Jones, Bill, author
Manchester University Press, 1991
Buku Teks