Since the early 1950s, two key partnerships have anchored stability and prosperity in the Indo-Pacific: the United States’ alliances with Japan and the Republic of Korea (ROK). Each grew from the devastation of war but matured into pillars of deterrence, economic growth and democratic resilience. Their enduring value is visible in the security architecture they uphold, the challenges they manage and the shared principles that guide them.
FORUM has chronicled these strengths over its 50 years of publication.
Japan-U.S. Alliance
The depth of the U.S. commitment to Japan’s defense under the 1960 Treaty of Mutual Cooperation and Security is demonstrated by the 55,000 U.S. military personnel stationed in Japan, and the thousands of civilians and family members who live and work alongside them. Japanese and U.S. forces have trained together since the late 1990s starting with the Keen Sword exercise. The U.S. deploys its most advanced military assets to Japan, including the USS Ronald Reagan carrier strike group and F-35 fighter jets.
The alliance has evolved into one of the world’s most capable and adaptable security structures. Over six decades, Japan’s Self-Defense Forces have grown into a technologically advanced organization that works seamlessly with U.S. forces across all domains. Forward-deployed U.S. personnel in Japan provide rapid response capability, while Japan’s logistical networks and sophisticated intelligence sharing underpin the regional posture.
From Cold War containment to modern deterrence against coercion in the East China and South China seas, the alliance has adjusted without losing coherence. It supports freedom of navigation, reinforces international laws and norms, and provides a foundation for the region’s economic vitality. The alliance’s values of transparency, democratic governance and commitment to peaceful dispute resolution sustain its credibility and influence.
In February 2025, the nations’ leaders stated their desire for continued growth in security and defense cooperation and reaffirmed that the Japan-U.S. Alliance remains the cornerstone of peace, security and prosperity in the Indo-Pacific.
ROK-U.S. Alliance
Born in the fire of the Korean War and codified in the 1953 Mutual Defense Treaty, the ROK-U.S. Alliance prevented the collapse of South Korea and has since been a foundation for Seoul’s economic and democratic successes. What began as a military partnership is now a comprehensive security framework covering nuclear deterrence, conventional force integration, cyber defense and humanitarian coordination, among other elements.
This alliance is defined by readiness and trust. ROK and U.S. troops train, plan and operate together at an elevated level of integration and about 28,500 U.S. military personnel are stationed in South Korea. Combined exercises hone rapid decision-making and interoperability, ensuring that deterrence remains credible against evolving threats. The alliance has expanded into technology cooperation, supply chain resilience and joint development of advanced capabilities.
In July 2025, senior officials from the nations met in Seoul to discuss strengthening the partnership into “a future-oriented, comprehensive strategic alliance, and to modernize the Alliance in a mutually beneficial manner in the face of an evolving regional security environment.”
Trilateral Strength
The shared sacrifice of generations of Japanese, South Korean and U.S. service members has prevented major conflict in Northeast Asia for more than seven decades, even amid significant strategic tension.
Japan and the ROK are essential partners for each other’s security, and trilateral cooperation with the U.S. magnifies deterrence and crisis-response capabilities. Recent coordination on missile defense, intelligence sharing and high-level diplomatic engagement highlights the growing synergy among the three democracies.
The nations’ foreign affairs chiefs met in October 2025 in Gyeongju, South Korea, to “underscore that deeper trilateral cooperation advances trusted economic leadership in the Indo-Pacific, tangibly benefits our shared economic well-being, and advances safety, security, and prosperity in a free and open Indo-Pacific,” the U.S. State Department said.
They also reiterated their nations’ commitment to the complete denuclearization of North Korea and the maintenance of peace and stability on the Korean Peninsula through dialogue and diplomacy.
Together, these enduring alliances form a strategic anchor for the Indo-Pacific. They protect trade routes, uphold international norms and provide stability so prosperity can flourish. After more than 70 years, their relevance continues to grow, evidence that shared values, backed by commitment, can shape a more secure and prosperous region.