Modelski postulates that the current nation-state system (dating from the Treaty Westphalia) can be characterized by cyclical trends in which "superpowers" progress from hegemonic status to overextension and deligitimation until the entire system degenerates in a global war which ushers in the era of a new superpower. On a purely aesthetic level, his argument has much appeal: it is easy to apply his basic arguments to underlying dynamics of the rise and fall of Spain/Portugal and Great Britain. One can even see where his arguments might apply to the United States' seeming demise as the most powerful actor in the international system today. Criticisms generally fall under two categories: methodological and historical relativism. Methodologically, one can argue that his theory lacks sufficient case studies to derive such a broad and sweeping explanation for such trends in the international system. Secondly, there are good arguments that the underlying tenets of his theory no longer apply in a world in which the superpowers have access to such overwhelming force as nuclear weapons that can be utilized to maintain their hegemony. Still, as a heuristic tool, it is a very cogent and parsimonious argument.