The international system consists of four types of states: those who have, those who used to have, those who are trying to have, and those who never had and never will have. The movement of history itself can be seen as a constant battle between conservative and revolutionary forces, between those seeking to maintain the established order and those seeking to revise it. We see this most clearly when international systems are in transition. At such times, world politics is defined by a competition among established and emerging powers over whose preferred order will prevail. Still, the emergence of rising powers does not inevitably trigger a revisionist-led struggle with the established powers over the fundamental nature of the existing order. The engine that drives the long cycle is the rise of a powerful revisionist challenger, dissatisfied not only with its place in the established order but also with the global order itself. Given the unlimited extent of its aims, the revisionist power cannot be appeased without undoing the existing international order. Unlimited-aims revisionists are rare beasts. Most revisionists can be accommodated or contained.