導彈防禦系統的建立與部署在直觀上係屬於傳統安全中的軍事議題，並反映了現實主義的嚇阻思維。但以全球或區域為範圍的導彈防禦若要能夠運作並發揮效能，缺少不了國家間的合作，也就是說現實主義的安全觀必須要透過自由主義下的互助與合作來落實。然而，即便國家間達成了共同建立導彈防禦系統的認知，但是對於「被防禦」的國家來說，卻意謂一項安全威脅的出現，因此勢必會設法與之周旋對抗，進而可能形成軍備競賽或是衝突對立的緊張關係，使得到頭來又是一種安全困境的呈現。
美國近年在歐洲的導彈防禦系統部署，為國際關係三個重要的理論：現實主義、自由主義、社會建構論，提供了檢驗的平台。透過觀察此系統部署過程中的主要當事方立場，本文發現社會建構論強調的「觀念」才是美國部署導彈防禦系統一系列政策的基礎，自由主義則是遂行此政策過程中的有效工具，至於現實主義不過是反射出美國的軍事強權及其定位敵我關係的安全觀，它很可能無助於國際社會或美國自身的安全，但可用以反省與檢驗部署導彈防禦系統一類的軍事安全政策，其實際有效性如何。

The establishment and deployment of Ballistic Missile Defense System (BMDS) is regarded as the military issue in traditional security and responds to the thought of deterrence in Realism. However, the context of the global ballistic missile defense regime could not be operated smoothly and effectively without transnational cooperation and mutual aid. In other words, the security framework of Realism must be implemented through the perspective of mutual aid and cooperation in Liberalism. In addition, given that the main countries achieve the cognition of establishing the BMDS, the opposite side, the defended countries, will regard it as a signal of security threat, and inevitably try to counteract it. The arms race or the conflict opposition tensions probably emerge and lead to a type of security dilemma presented eventually.
Washington reaching its long-term goal of setting up a BMDS in Europe recent years has provided the examination platform in the thoughts of Realism, Liberalism, and Social Constructivism. This article penetrates the processes of US system deployment and all standpoints to demonstrate that Social Constructivism is a guiding ideology and the Liberalism is the effective tool to carry out the processes of this policy. As for the Realism, it is a consequence of revealing to the world. It possibly not helps to guarantee the international society or the US itself security but to examine the validity of military security policy.