editorial information compiled by the Economist
The Economist Newspaper Limited, 1984
Buku Referensi
World Bank
World Bank, 1981
Buku Teks
MacKay, R.A.
The Ryerson Press, 1935
Buku Teks
Routledge, 1992
Buku Teks
edited for the Society of American Historians by Courtlandt Canby & Nancy E. Gross
New American Library, 1954
Buku Teks SO