System and Process (1957) broke the mould in political science by combining systems, game, and cybernetic concepts in its theoretical formulations. Since its publication, serious research in international relations has needed to respond to the bold hypotheses that matched equilibrial rules with type of system. Kaplan's life-long interest in finding an objective basis for moral judgments had its scholarly origins in an appendix of this classical book, which incorporated his understanding of philosophy and, in particular, the philosophy of science. A second appendix on 'The Mechanisms of Regulation' explored the cybernetic and recursive nature of knowing.
[Kaplan’s book] points like all good theory, from the actual to the potential... and it may help to liberate us from bondage... either to a moralism which undercuts itself by denigrating the means necessary for maintaining values or to an opportunism which continually degrades the values of the political and social system in the guise of defense of the system.
Kaplan’s book may, with some justification, be called the first professional book on International Relations.
Every profession is occasionally inflicted with challenges that loom large.... in economics these would include Keynes’ General Theory, Hicks’s Value and Capital, [and] Samuelson’s Foundations.... In short, Kaplan’s book is a must.
In the history of the subject, [Kaplan’s book] may come to mark the epoch at which we got beyond prolegomena and began to develop a truly general theory.