The Rapprochement Between South Korea and Japan in the Context of the North Korean Nuclear and Missile Threat

This thesis investigates the political and security rapprochement between South Korea and Japan from 2015 to 2025 in the context of the escalating North Korean nuclear and missile threat. The study is anchored in a neorealist framework and employs Stephen M. Walt’s balance-of-threat theory to show how variations in perceived threat shape state strategic behaviour. The findings indicate that South Korea pursues a dual strategy of external balancing (most notably through trilateral cooperation with the United States and Japan) and internal balancing through military modernization and the expansion of its domestic defence industry. The empirical analysis demonstrates that although South Korea confronts a range of security challenges, including China’s increasing assertiveness and broader regional instability, the North Korean threat constitutes the primary driver of deepening cooperation with Japan. The thesis concludes that, while the North Korean nuclear and missile threat alone is insufficient to produce full political convergence, under favourable conditions it can nonetheless facilitate the overcoming of long-standing historical and political obstacles to closer bilateral and trilateral collaboration.