1. David Easton, The Political System: an Inquiry into the State of Political Science (New York: Knopf, 1964), p. 130.
2. Harold D. Lasswell and Abraham Kaplan, Power and Sociey: A Framework for Political Inquiry (New Haven: Yale University Press, 1950), pp. 55–57 and passim.
3. These rough figures are adequate for present purposes. For more precise figures and a view of the complexities involved in ascertaining them, see Michael D. Wallace and J. David Singer, “Intergovernmental Organisation in the Global System, 1815–1964: A Quantative Description,” International Organisation, 24 (Spring 1970), 239–287. Lists of existing IGOs and INGOs that include a brief statement about each organisation are published by the Union of International Associations in the periodic editions of the Union’s Yearbook of International Organisations....
4. Again achieving a precise count is complicated. For careful efforts see G.P. Speeckaert, The 1,978 International Organisations Founded Since the Congress of Vienna. A Chronological List (Brussels: Union of International Associations, 1957),
5. and Kjell Skjelsbaek, “The Growth of International Non-governmental Organisation in the Twentieth Century”, International Organization 25 (Summer 1971), 420–422.