MOSCOW -- The role of nuclear weapons is undergoing subtle but important changes in deterrence strategy. Although this transformation is a consequence of the collapse of bipolarity in international relations and the shift in military threats from the global to the regional context, the trend is becoming more visible as a result of recent developments. The principles of nuclear deterrence are beginning to alter in a way that could have a profound impact on the still-evolving post-Cold War security order.

This transformation is visible in the current U.S. debate on a national missile defense system. The political debate has narrowed to when and how -- rather than whether -- the United States should deploy such defenses. At the core of the debate is a growing acknowledgment that deterrence in the 21st century cannot be based on principles that were the foundation of the now-gone Cold War nuclear paradigm.

Traditionally, deterrence has been an offense-based posture that aimed at retaining a balance between mutual vulnerabilities and the capacity to wreak unacceptable punishment on an aggressor. Now, national and theater missile defenses symbolize a potential shift in focus from offense to defense. Without abandoning offense, deterrence will instead be constructed on defensive capabilities that will tilt the balance between mutual vulnerabilities in favor of one side.