Griffiths, Martin
Routledge, 1992
Buku Teks
Callahan, David
Harper Collins , 1994
Buku Teks
Chandra, Prakash
Vikas Publishing House, 1982
Buku Teks
Chandra, Prakash
Vikas Publishing House, 1982
Buku Teks
Holsti, Kalevi J.
Prentice-Hall, 1977
Buku Teks