均衡理論 (バランシング・セオリー) から見た米国一極体制

冷戦後世界とアメリカ外交

抄録

This paper aims to explore how states' balancing behaviors have changed in the transition from the bipolarity during the Cold War period to the unipolarity in the post-Cold War period. Whether or not unipolarity is sustainable is still controversial. Structural realism argues that unipolarty is not sustainable, because unipolarity is an imbalanced international system where the superpower monopolizes most of economic and military capabilities and other major powers are likely to balance against the superpower to restore the balance-of-power within the system. However, the unipolarity in the post-Cold War period has not only continued for more than fifteen years but also intensified the concentration of economic and military strength on the United States (U. S.). Also, other major powers have neither built up military strength nor formed an alliance against the U. S. yet. Why have not non major powers attempted to balance against the U. S. and restore the balance of power? Could unipolarity be a sustainable international structure? This paper explores conditions under which the U. S. is likely to sustain the unipolar system without much resistance from other major powers and conditions under which states are likely to balance against the U. S. Basically, the paper argues that whether or not a unipolar system can be sustainable depends on behaviors of the superpower. Although many claim that U. S. should restrain its aggressive foreign policy, this paper asserts that the strategic restraint is necessary but not sufficient for maintaining the unipolarity. The U. S. should continue to provide international public goods to the international society, because the provision of public goods gives incentives for other states to support the U. S. -led unipolar system and makes the unipolarity durable. Then, the paper further attempts to compare predictions and implications of this main proposition with those of the balance-of-power theory and the balance-of-threat theory and illuminate their differences. Examining trends of economic and military capabilities among major powers, threat perceptions toward the U. S., and behaviors of major powers in international organizations and regimes in the post-Cold War period, this paper concludes that the current Bush administration's foreign policy is worrisome but not so threatening to other states to such an extent that they attempt to balance against the U. S. Finally, the paper suggests that it is critical to further assess and determine whether the Bush administration's behavior shows the aberration of U. S. international cooperation policy during the former Bush and Clinton administrations, or the starting trend of the U. S. unilateral foreign policy in the long run for the future.