Long-standing security alliances with Japan and the Republic of Korea have been a cornerstone of U.S. engagement in Northeast Asia and with the broader Asia-Pacific region. “Boots on the ground” ensured that Washington stayed deeply involved in Asian affairs and remained attuned to regional developments. Those alliances have come under increasing scrutiny as the regional security environment has evolved. Critics charge their raison d’etre has vanished with the dissolution of the Soviet Union and that their continued existence – as currently configured – is problematic for regional security: China fears that instruments once designed to deter a Soviet threat will be deployed against it. Beijing’s antipathy to those alliances – its calls them “outdated relics of the Cold War” – influences the thinking of U.S. allies as they contemplate their relationships with Washington.