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..

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 distribu..