同盟安全与防扩散——美国延伸威慑的可信度及其确保机制

冷战以来,美国就始终坚持推行延伸威慑战略,并将其视为最重要的防扩散工具之一。然而,这种基于经验的政策逻辑缺乏系统性的理论支持。获得美国延伸威慑保护的国家或约束自己的核扩散行为,或走上研发核武器的道路,抑或推行两面下注的"核避险"战略。在获得延伸威慑保护与核不扩散行为之间,并未呈现出简单的因果关系。因此,延伸威慑究竟是不是一种有效的防扩散手段以及在何种条件下才能起到防扩散的作用,便是值得深入探讨的问题。在控制外部威胁以及供给侧因素等干扰变量之后,本文发现延伸威慑的可信度是影响受保护国核扩散行为的中间变量。而可信度的变化又与美国和盟友之间建立起来的一系列确保机制相关。确保机制包括口头或书面承诺、前沿部署、核分享以及核磋商这四类措施。不同的确保措施对延伸威慑可信度的影响不同,同时也会对美国在核安全以及受牵连的问题上造成相应的影响。因此,美国及其盟友往往在确保机制的选择上有着不同的利弊偏好。冷战时期,联邦德国和韩国在同时受到外部安全威胁和美国延伸威慑保护的情况下,却采取了不同的核扩散行为,对此延伸威慑可信度及其确保机制理论做出了合理解释。总体上,由于美国与不同盟友所建立的确保机制不尽相同,从而使得延伸威慑的可信度出现差异,并最终导致盟友之间出现不同的核扩散行为。

Alliance Security and Nonproliferation:The Credibility of the U.S.Extended Deterrence and Its Assurance Strategy

Since the Cold War,the United States has pursued the extended deterrence strategy and regarded it as one of the most important non-proliferation tools.However,not all countries that have obtained the U.S.extended deterrence protection have restricted their nuclear proliferation.Some have embarked on the path of developing nuclear weapons or have pursued the"nuclear hedging"strategy.There is no simple causal relationship between the acquisition of extended deterrence protection and nonproliferation.Therefore,whether extended deterrence is an effective means of nonproliferation and under what conditions it can play a role in nonproliferation are questions worthy of in-depth discussion.After controlling the external threats and supply side factors,this paper finds that the credibility of extended deterrence is an intermediate variable that affects the nuclear proliferation behavior of protected countries.The variation in credibility is related to a series of assurance mechanisms established between the United States and its allies.The assurance mechanisms include oral or written commitments,forward deployment,nuclear sharing and nuclear consultation.Different assurance measures have different effects on the credibility of extended deterrence,and produce corresponding impacts on the U.S.nuclear security and entrapment issues.Therefore,the United States and its allies often have different preferences in choosing assurance mechanisms.During the Cold War,the Federal Republic of Germany and the Republic of Korea adopted different nuclear proliferation policies while they both faced external security threats and obtained extended deterrence protection from the United States.Such cases can be accounted for by the theory of extended deterrence credibility and its assurance mechanisms.In sum,different assurance mechanisms established by the United States with its allies lead to different credibility of extended deterrence,and hence different nuclear proliferation behaviors among the U.S.allies.