The Philippines and Japan are deepening their defense cooperation, now considering the South and East China Seas as a single, interconnected security challenge. This “one theater” concept reflects growing concerns over China’s increasing assertiveness in both maritime regions. The shift signifies a broadening of the two nations’ security outlook, moving beyond traditional bilateral focuses. Officials indicate this integrated approach will inform future joint exercises and strategic planning. This development comes as both countries strengthen alliances with the United States and other partners in the Indo-Pacific. The move aims to enhance regional stability and deter potential aggression, acknowledging the overlapping security dynamics in the contested waters. This collaborative strategy underscores a unified response to shared security concerns.