Comments by influential South Koreans that their country should consider requesting the return of US nuclear weapons to their shores—or even acquire its own nuclear weapons—reflects persistent unease about how regional security developments are challenging US extended security guarantees developed during the Cold War.
In the case of South Korea, the United States pledged through a bilateral mutual defence treaty to help defend the country from an external attack, presumably from North Korea, with nuclear weapons if necessary. The deployment of sizeable US conventional forces in South Korea was aimed at making these extended security guarantees more credible.
The effectiveness of deterrence is difficult to prove, since by definition nothing happens. If a country is deterred from attacking, it is a non-event. Sceptics can plausibly argue that perhaps the presumed aggressor never intended to attack, or at least refrained from the assault for other reasons. Still, the North Korean invasion of the South was never repeated, perhaps due to US threats to retaliate—something that was lacking before June 1950.
Extended deterrence is a function of capacity, will, and perception. It requires that the guarantor has the capacity to defend another country under attack as well as the intent to do so, and this capacity-will combination must be perceived by the target as sufficiently strong that the potential aggressor decides to refrain.
In addition to deterring a potential aggressor through threats of retaliation, a deterrence pledge also involves an assurance dimension. The state receiving the guarantee must perceive it as credible given the guarantor’s capacity and will. Otherwise, it will seek to appease the potential aggressor—or balance the threat through unilateral action.
In the case of South Korea, the means of unilateral balancing under consideration has extended to include nuclear weapons. During the Cold War, the United States stationed hundreds of nuclear weapons there. At times, early South Korean governments contemplated and even started nuclear weapons programmes.
The Cold War has ended, and the Pentagon removed all US nuclear weapons from South Korea two decades ago. But the commitment to defend the country with nuclear weapons if necessary is still seen as essential to keep South Koreans from losing faith in the US willingness or capacity to defend them.
In one of his last public speeches in Asia before leaving office, then US Secretary of Defense Robert Gates acknowledged to participants at the Shangri-La Dialogue in Singapore that several developments relating to North Korea were making the East Asian strategic environment more dangerous.
First, North Korea’s indiscriminate selling of items useful for making nuclear weapons or ballistic missiles was destabilizing ‘the entire region.’ Second, the US homeland was for the first time becoming vulnerable to a direct North Korean attack. Gates related that he and President Barack Obama had told Chinese leaders several times that North Korea’s continued progress in developing long-range ballistic missiles armed with nuclear warheads was becoming a ‘direct threat to the United States.’
In addition, the risks had increased that any further North Korean provocations against South Korea would rapidly escalate into an armed confrontation between the two parties. Gates also warned that North Korea’s outrageous provocations against the South last year—sinking the Cheonan and shelling civilians on a border island—had so roused South Korean opinion that vigorous retaliation to any further provocations was much more likely. ‘And one of the worries we have dealt with over the last seven or eight months, both with our friends in the Republic of Korea and also in our dialogues with our Chinese friends and other members of the Group of Six is the danger of unpredictable escalation in the event of another provocation,’ he noted.