Because of its internal coherence, long history of empirical validation, and wide range of excess empirical content compared to competitor theories of world politics, I center my efforts in this book around a theoretical revision of power transition theory intended to permit analysis of minor power international relations. I call my revision of power transition theory the “multiple hierarchy model.” Power transition theory describes the international system as an international hierarchy of power. My revision recasts the international system as a series of parallel power hierarchies, each of which functions similarly to the others and to the overall international power hierarchy. The revision highlights the existence of sub-systems within the overall international system. In purely technical terms this may seem a modest revision. But I very much hope the reader will not dismiss my revision as too modest to be of interest. Oaks grow from acorns, after all, and I suggest the discussion hinted at in chapter 1, and returned to in chapters 5 through 7, augurs well that a rather mighty theoretical oak will grow from the acorn of the multiple hierarchy model. In the following pages I describe in detail what the multiple hierarchy model is, how it differs from traditional power transition theory, and what specific hypothesis follows from it. I then trace some of the intellectual history of the notion of sub-systems, subordinate state systems, and regional systems in an effort to provide some sense of the plausibility of a theoretical revision along these lines.