While few believe Kim Jong Un would launch an unprovoked nuclear strike, most seasoned Korea watchers believe that he would no doubt use his arsenal once it became clear he was about to lose any war that broke out. As this risk increases, Washington will find it increasingly difficult to avoid reassessing the country’s multi-decade alliance with South Korea. The threat to American civilians will be magnified to grotesque proportions, simply because Washington continues to promise to help South Korea.
At stake is not just Washington’s commitment to Seoul, but, quite possibly, America’s larger global standing.
The arguments for maintaining a strong South Korean alliance rest on its deterrent effect against North Korea. The Kim regime has repeatedly struck out at the South—see the 2010 sinking of the Korean navy vessel Cheonan that killed 46 sailors and the shelling of Yongpyong Island. Yet the North has refrained from large-scale attacks against either South Korea or Japan, another target of Pyongyang’s ire, despite its significant missile capability and larger military. Washington interprets this as due, at least in part, to the assumption by all parties that a major attack, or full-scale war, would immediately trigger the self-defense clause of the mutual defense treaty between the United States and South Korea. If that is the case, then the U.S. commitment will be even more important: Only a firm U.S. promise to defend the South will deter the North.
But if, on the other hand, the United States decided that the risk to its interests was prohibitively high, abrogating or scaling back the alliance would potentially destabilize Asia and beyond. It would hand the Kim regime a major strategic victory, removing the single greatest deterrent to its aggression. Pyongyang would be emboldened to continue trying to blackmail the United States, South Korea, and Japan, leading to future crises. Stripped of the assurance provided by America’s support, South Korea might wind up capitulating to the North’s demands for open-ended economic assistance, or even stand down some of its forces. Japan would worry that it may be the next to be abandoned by America. Even worse, in the face of a U.S. withdrawal, both Seoul and Tokyo would immediately begin considering developing their own nuclear and missile programs, instigating a nuclear-arms race that would spill over to China, Taiwan, and possibly beyond.
In the event of a reduced American presence in northeast Asia, China would emerge the big winner. Beijing almost certainly would offer Seoul an alliance of its own, further undermining America’s regional web of alliances, likely tipping the Philippines and Malaysia fully into the Chinese camp. Japanese government officials I spoke to expressed their fears that, in the event of the collapse of the U.S.-South Korea alliance, Beijing may even base Chinese warships in Busan, the southern port closest to Japan, giving China a foothold on the territory closest to the Japanese home islands—historically, Japan’s major geopolitical fear. Access to the southern Korean coastline would enhance China’s ability to control the strategic waterways from the South China Sea through the East China Sea and into the Sea of Japan. The Japanese would consider this a grave threat. In response, the U.S. resources diverted from the Korean peninsula might be redeployed to blunt China’s expansion, including a beefing-up of the U.S. Navy in Japan, which would increase Sino-U.S. tensions and the potential for a maritime confrontation in the narrow, strategic Tsushima Strait.