Since its founding, South Korea's overriding external problem has been North Korea, as the threat of renewed aggression has never been wholly lifted. From time to time this theoretical threat has also been reinforced by acts of terrorism by North Korea against South Korea. The most notorious cases of such acts were the assassination of 16 prominent South Koreans, including four members of South Korea's cabinet, by North Korean agents in Burma in October 1983 and the bombing by North Korean agents of a Korean Air passenger aircraft in September 1987, which killed all 115 people on board. More recently there have been several instances of violations of South Korean territory by North Korean submarines, fishing boats and surface vessels.

Military forces in the region, 2001/02

South Korea North Korea Japan China Russia Army Personnel Main battle tanks 560,000 2,330 950,000 3,500 148,700 1,050 1,600,000 8,000 321,000 21,820 Navy Personnel Frigates Submarines 60,000 9 19 46,000 3 26 44,200 12 16 250,000 41 69 171,500 10 56 Air force Personnel Combat aircraft 63,000 555 86,000 621 45,400 297 420,000 2,900 184,600 27,636

Source: International Institute for Strategic Studies, The Military Balance 2001/2002.

The Korean Peninsula is one of the most heavily militarized areas in the world. North Korea's armed forces are positioned forward for a blitzkrieg attack on South Korea, while South Korean forces are deployed in order to repel them. South Korea's capital, Seoul, in which around one-quarter of the population lives and which the North has threatened to turn into a "sea of flames" is particularly vulnerable, being so close to the DMZ; military experts suggest that it would take Northern bombers less than three minutes to reach the center of Seoul, from the DMZ. As long as an aggressive communist regime survives in North Korea this is likely to remain the case, although limited economic exchanges and continuing diplomatic co-existence, particularly since the mid-2000 inter-Korean summit, should help reduce tension.

Although South Korea has been spending less than 3% of GNP on defense, it has been closing the military gap. North Korea spends up to 25% of its much smaller GNP on defence. Although North Korea's quantitative lead in numbers of troops, tanks, submarines and aircraft remains a worry, this is balanced now by South Korea's qualitative lead. There is also concern, however, over North Korea's development of missiles and suspected stockpiles of chemical and biological weapons, as well as lingering doubts about its nuclear program. Concerns over the latter came to a head in early 1994 when North Korea resisted inspections of its nuclear sites by the International Atomic Energy Agency (IAEA) and reneged on its obligations under the nuclear non-proliferation treaty. The crisis culminated in the October 1994 Agreed Framework, under which North Korea would receive two light-water reactors from the West in return for freezing its nuclear program. Despite the agreement, concerns were unabated, about Pyongyang's nuclear ambitions. In October 2002, North Korea admitted that it had carried on its nuclear arms development programs and expelled IAEA monitors from its nuclear project sites in Yeongbyeon, creating new tensions. International pressures mounted to make North Korea to abandon its nuclear programs in exchange for economic aid.

The world community now sees South Korea as a country blessed with democracy and marked degree of freedom. Korea is to enhance its maturing political system with an equal eye toward liberalizing the economy. The Republic of Korea endeavors to develop diplomatic policies that will help win international support for its security posture and for the peace and stability on the Korean Peninsula. The Republic has, over the years, maintained and strengthened security cooperation with the United States designed to sustain a credible military deterrent. South Korea's new ties with China and Russia, the North's former military allies, have triggered vast changes in the international arena. China and Russia no longer automatically support North Korea's positions.

The Republic of Korea has increased its national defense capability by emphasizing self-reliance. This increased military strength, coupled with the stationing of U.S. military forces in the South, has helped to diminish the threat of a North Korean military provocation.