This paper investigates the evolving North Korean nuclear threat and its implications for the ROK-U.S. alliance. Examining North Korea's nuclear trajectory, it highlights the severe challenges posed by its advancements in nuclear and missile technology. While the ROK-U.S. alliance has been historically strengthened in response to this threat, recent shifts in regional dynamics, including the intensifying U.S.-China competition, necessitate a reassessment of alliance development strategies. The analysis identifies a critical need to address differences in threat perception between the allies, driven by North Korea’s increased missile tests and ICBM advancements, which cast doubt on the effectiveness of existing deterrence posture. The study emphasizes that aligning ROK-U.S. strategic priorities and upgrading extended deterrence mechanisms are essential for continuous development of the alliance despite North Korea’s nuclear capabilities. Additionally, the findings suggest that enhancing military and technological inter-operabilities within the alliance, along with an adaptable extended deterrence strategy, will be vital to maintaining regional stability.