This pathmaking treatise on macrotheoretical science argues that a brink separates an explanatory theory of international politics from those approaches that lack basic standards for theoretical construction—a brink which must be bridged if the discipline is to develop. Formulated on the basis of a pragmatic philosophy of science, its most general arguments cross the boundaries of the social sciences, including the standard subdisciplinary boundaries of international relations. Although the substantive theories in the book tend to be about systems usually characterized as power politics, the basic approach and categories could be used to analyze systems of international political economy, international organization, or comparative politics.