US-ROK

The US-ROK (United States–Republic of Korea) relationship is a treaty alliance anchored by the 1953 Mutual Defense Treaty, under which the US maintains approximately 28,500 troops on the Korean Peninsula and commits to South Korea's defence against external attack. The alliance encompasses joint military operations, intelligence sharing under the Five Eyes-adjacent framework, combined exercises, extended nuclear deterrence commitments, and interoperability agreements covering ground, air, maritime, and increasingly, cyber and space domains. The relationship is managed through the Security Consultative Meeting (SCM) at ministerial level and the Military Committee Meeting (MCM) at chiefs-of-defence level.

The cyber dimension of the alliance has grown significantly since the 2014 Sony Pictures attack and repeated North Korean cyber operations against South Korean financial and critical infrastructure. The two nations share threat intelligence on DPRK cyber actors through bilateral channels and coordinate on attribution. However, as of 2026, the alliance has not formalised an operational cyber posture — the capability to Conduct joint offensive or active-defence cyber operations against shared adversaries — in the manner that Five Eyes nations have moved toward.

In U#3, the Center for Strategic and International Studies (CSIS) published a paper on 7 May 2026 calling for the US and South Korea to move from intelligence sharing to an operational cyber alliance posture , explicitly modelling the recommendation on the Five Eyes operational convergence. The paper reflects a wider debate within alliance management about whether the US-ROK cyber relationship is keeping pace with the shared DPRK and PRC threat environment.