Kaplan introduced a new analytical tool to the study of international relations, systems analysis.
[3] His view contrasts with that of John Rawls - that it might be possible to isolate some basic social and political rules; rather Kaplan's alternative theory of justice is his test in principle, a kind of decision procedure for evaluating social, political, and moral choices, which attempts to circumvent the limitations of an egocentric or culturally narrow perspective while providing sufficient context to make a judgment.
[4] Kenneth E. Boulding and Charles Kindleberger gave Kaplan's System and Process in International Politics negative reviews.
[5] Kindleberger argued that the book was a "must" read and that the primary contribution of the book was Kaplan's discussion of the international system and balance of power, but he argued that Kaplan's work did not lend itself to empirical testing, and that the application of game theory to politics and conflict was problematic.
Katzenbach in 1961 where they write, To understand the substance and limits of such constraining rules (international law), it is necessary to examine the interests which support them in the international system, the means by which they are made effective, and the functions they perform.