This special issue examines the strategic choices and policy options for South Korea and the US in responding to North Korea’s rising security challenges. With President Trump back in office and shifts in policy priorities, South Korea currently faces difficulties in establishing credible deterrence measures against North Korea. This introductory article provides theoretical discussions on nuclear deterrence and explores the complexities of achieving deterrence within the framework of asymmetric alliances, in which actors have the alliance dilemma―abandonment and entrapment risks. To better understand the three articles in this special issue, these theoretical discussions provide readers with necessary context, addressing various aspects of the alliance dilemma, public support for foreign policies, and alternative deterrence policy options, such as independent nuclearization and nuclear sharing agreements.