In South Korea, the South Korean military is responsible for external defense and is primarily focused on the threat from North Korea; it participates in bilateral and multinational exercises and deploys abroad for international missions, including peacekeeping and other security operations

South Korea's primary defense partner is the US, and the 1953 US-South Korea Mutual Defense Treaty is a cornerstone of the country's national security; the Treaty committed the US to provide assistance in the event of an attack and gave the US permission to station land, air, and sea forces in and about the territory of South Korea as determined by mutual agreement; South Korea hosts approximately 28,000 US military troops and regularly conducts bilateral exercises with the US military; South Korea has Major Non-NATO Ally (MNNA) status with the US, a designation under US law that provides foreign partners with certain benefits in the areas of defense trade and security cooperation; the South Korean military has assisted the US in conflicts in Afghanistan (5,000 troops; 2001-2014), Iraq (20,000 troops; 2003-2008), and Vietnam (325,000 troops; 1964-1973)

in 2016, South Korea concluded an agreement with the EU for participation in EU Common Security and Defense Policy (CSDP) missions and operations, such as EU counter-piracy operations off the coast of East Africa; South Korea has had a relationship with NATO since 2005, and in 2022 established a mission to the NATO headquarters to further cooperation; it has participated in NATO-led missions and exercises, including in Afghanistan and the Gulf of Aden (2025)