In South Korea, the South Korean military is primarily focused on the threat from North Korea; it also deploys abroad for multinational 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; the US maintains approximately 28,000 military personnel in the country and conducts bilateral exercises with the South Korean 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 the EU Naval Force Somalia – Operation Atalanta, which protects maritime shipping and conducts counter-piracy operations off the coast of East Africa

South Korea has been engaged with NATO through dialogue and security cooperation since 2005 and is considered by NATO to be a global partner; in 2022, South Korea established its Mission to NATO to further institutionalize its cooperative relationship; it has participated in NATO-led missions and exercises, including in Afghanistan as part of the NATO-led International Security Assistance Force, 2010-2013; it has also cooperated with NATO in countering the threat of piracy in the Gulf of Aden by providing naval vessels as escorts

in addition to the invasion of South Korea and the subsequent Korean War (1950-53), North Korea from the 1960s to the 1980s launched a considerable number of limited military and subversive actions against South Korea using special forces and terrorist tactics; including aggressive skirmishes along the DMZ, overt attempts to assassinate South Korean leaders, kidnappings, the bombing of an airliner, and a failed effort in 1968 to foment an insurrection and conduct a guerrilla war in the South with more than 100 seaborne commandos; from the 1990s until 2010, the North lost two submarines and a semi-submersible boat attempting to insert infiltrators into the South (1996, 1998) and provoked several engagements in the Northwest Islands area along the disputed Northern Limit Line (NLL), including naval skirmishes between patrol boats in 1999 and 2002, the torpedoing and sinking of a South Korean corvette, the Cheonan, in 2010, and the bombardment of a South Korean Marine Corps installation on Yeonpyeong Island, also in 2010; since 2010, further minor incidents continue to occur periodically along the DMZ, where both the North and the South Korean militaries maintain large numbers of troops; ; in late 2023 and early 2024, the Kim regime abandoned decades of official policy and declared that South Korea was not inhabited by “fellow countrymen” but a separate and “hostile” state that the North would “subjugate” if war broke out (2024)