IN THE EARLY DECADES OF THE TWENTY-FIRST century, relations among the nations of East Asia may be characterized by high and rising levels of economic interdependence, expanding cooperation in a lengthening list of international institutions, growing trust and a deepening and ever more stable peace. Or, on the other hand, they could be marked instead by mutual suspicion, shifting diplomatic alignments, arms races, crises, and periodic wars. While many observers hope that Asian international politics in the years ahead will resemble the patterns that have come to prevail in Western Europe in the second half of the twentieth century, skeptics fear that they may be more similar to those that marked the previous four hundred years of modern European history. The way different observers characterize the future of East Asian security depends, among other things, on their beliefs about the fundamental character of world politics and the relative strength of the contending forces that are reshaping the international system. Although it is not always couched in these terms, the debate over Asia's future is, at base, a dispute between adherents to very different theories of international relations. Whether or not they identify themselves with such labels, those who are most pessimistic tend to be guided in their thinking by the tenets of political "realism" while those who take a more optimistic view are usually recognizable either as "liberals" or as what are referred to in contemporary academic jargon as "constructivists."