Santoro, David, and John K. Warden

Abstract
Discussions about the requirements for U.S. extended deterrence and assurance are making a comeback. During the Cold War, U.S. analysts focused primarily on Western Europe, but in recent years the challenges of extended deterrence and assurance have been starker in Northeast Asia. Discussing the requirements for U.S. extended deterrence and assurance involves asking how the United States can deter its adversaries and assure its allies. In both cases, the critical factor is perception. According to analysts Clark Murdock and Jessica Yeats, “In the same way that deterrence must be tailored to each actor, situation, and form of warfare, assurance must be tailored to the strategic culture, threat perceptions, values, and specific concerns of each ally.”1
In this paper, we primarily address the requirements of the latter, focusing on U.S. efforts to assure its two Northeast Asian treaty allies: Japan and South Korea. After analyzing the current security environment—specifically the assurance requirements in Northeast Asia in this second, post-Cold War nuclear age—we turn to the initial steps that the United States has taken to strengthen assurance. Finally, we explore the current assurance agenda with Japan and South Korea, highlighting key challenges and opportunities.
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