The balance of power constitutes one of the central concepts in Hans J. Morgenthau's Politics Among Nations where it is depicted as ‘a necessary outgrowth of power politics’ (Morgenthau, 1973: 167). It is over half a century since Morgenthau first wrote Politics Among Nations and over thirty years since he produced the fifth and, for Morgenthau, final edition. It is, therefore, a quintessentially cold war text. But it is clear that Morgenthau intended to provide a general theory for students of international politics, and one that would stand the test of time. From the start, however, Morgenthau's attempt to provide a general theory came under fire from many quarters and his concept of the balance of power, in particular, is often severely criticized for being ahistorical, ambiguous and incoherent. Nevertheless, subsequent realists have continued to insist that the balance of power is an intrinsic feature of international politics and that any general theory must take account of the concept. These later realists, however, step back from Morgenthau's very comprehensive approach and refine the concept in an attempt to overcome problems of ambiguity and incoherence. In this process of distillation, however, realism has become increasingly fragmented, with the additional consequence that Morgenthau's approach to the balance of power remains much more expansive than the balance of power theories developed by Waltz (1979) and Mearsheimer (2001) that are discussed in Chapters 6 and 7.