在一個以美國為首的後冷戰單極國際體系中，次級強權與美國之間的動態性權力安排，將直接影響單及體系是否得以續存。傳統國際關係理論主張「權力平衡」是維持國際社會與區域安全的穩定要素，但該理論針對的是強權間為維持軍事戰略利益，所採取以軍事力量作為手段的平衡關係，對於後冷戰時期美國與其他次級強權的互動，似乎缺乏解釋的效力。在這些次級強權當中，歐洲聯盟扮演一個非常特殊的角色。歐洲與美國同享重要的文化與宗教價值，但在具戰略意義的議題上，兩者的歧見卻益形明顯。歐盟在重大國際議題上與美國的背道而馳，已形成對於此一超強的抗衡作用，但是傳統強調軍事力量的「硬性平衡」概念，無法有效解釋歐盟所發揮以軍事以外手段進行對美國的平衡。本文試圖提出「柔性平衡」的相對概念，亦即次級強權試圖以軍事力量以外的手段，獲致抗衡超強達成其戰略利益的目的，並以此來檢驗歐洲與美國在後冷戰時期的關係，是否存在系統性的柔性平衡。本文首先強調傳統權力平衡理論再解釋後冷戰時期單極體系的不足，並提出以柔性平衡的論述做為補充；在實際的個案方面，本文特別著重在歐洲聯盟於後冷戰時期與美國在重要國際議題上的歧異，並因此檢驗是否形成對美國的柔性平衡策略；本文在結論部分，除了試圖在理論的層次，提出柔性平衡對於權力平衡理論的適用與補充之外，也期待在政策方面，提出次級強權的個別或連可能藉由柔性平權方式，產生對於新時期國際體系可能轉換的影響。

In a U.S.-dominated post-Cold War unipolar international system, the possible power shifts between the second-tier great powers and the Americans, such as a systemic balance, will have great impacts on the existence and endurance of the current international system. According to the Realist theses, “balance of power” is a stabilizing factor that contributes to international security and regional stability as the great powers endeavor to prevent concentration of capabilities in one or a few nations through the process of distribution of power. However, it seems questionable when the conventional “balance of power" thesis, focusing exclusively on military balancing as a means to maintain military and strategic interests among the great powers, is applied to the interrelationship between the U.S. and its junior counterparts in the post-Cold War era. Among the post-Cold War second-tier great powers, the European Union plays a very special role. Despite the fact that the Europeans share key cultural and religious values with the Americans, the EU has gradually developed its own global strategic status by expanding the multiple dimensions of power, including its adherence to multilateralism that places the EU in opposition to the U.S when dealing with crucial global affairs. While the Europeans might place in harmony with the Americans on some global issues in the Cold War era, their differences over major disputes appear much more unbridgeable than ever before. The fact that the EU and the U.S. have been divergent on key international issues indicates that some form of balance may be emerging Yet, the conventional “hard balancing" theory cannot explain the non-military balancing exercised by the EU vis-à-vis the U.S. This article attempts to propose the “soft balancing” thesis, referring to a means used by the second-tier great powers that take non-military measures to achieve strategic interests by balancing the super power. The paper’s main purpose is to examine relations between the EU and the U.S. in the post-Cold War era in order to understand whether a soft balancing relationship between the two exists. This article begins by discussing the major theses proposed by the Realist “balance of power” theory, followed by the counter-proposal of “soft balancing” put forward in the post-Cold War era. It then examines some key international issues where the EU and the U.S. have had divergent positions, with an aim at finding the pattern of EU’s soft balancing vis-à-vis the U.S. The article concludes by proposing the applicability of the “soft balancing” thesis on the theoretic level, as well as its implications for policy-making concerning the impacts that the emerging soft balancing in an individual or a collective manner would have on the international system as a whole.