The Evolutionary Logic and Development Trend of South Korea's "ROK-US-Japan Trilateral Security Cooperation" Policy

Trilateral security cooperation (TSC) between the Republic of Korea, the United States, and Japan has gradually entered a new stage of comprehensive development. From South Korea's perspective, the "North Korean issue" and "ROK-Japan historical conflicts" are key factors affecting the progress of TSC. However, the existing research either emphasizes the dominating role of the United States, or lists the issues that influence the TSC policy choice, but few explore the causal mechanisms between these issues and TSC policy choices. To explain the causal mechanisms underlying the evolution of South Korea's TSC policy, this paper considers both systemic and unit-level variables, proposing a neoclassical realist analytical framework and testing it through the case of South Korea's TSC policy. System-level pressure, perception of external threats, national strategic preferences, and domestic cohesion level are four main variables that have influenced South Korea to strengthen security cooperation with the United States and Japan, and they are also critical components of causal explanations. Among them, threat perception and strategic preferences have the potential to change, while the degree of domestic division will constrain the further development of future TSC. This study employs foreign policy theories from the actor-centered perspective and their interaction will provide and complement the explanation of TSC.