Fifty years after the establishment of official diplomatic relations between Japan and South Korea, continued animosity between the United States' two Northeast Asian allies remains a problem for Washington, hampering its ability to deal with the challenges posed by North Korea, China, and a host of nontraditional security threats. Mutual suspicion and mistrust between Tokyo and Seoul, fueled by disputes over territory and history, jeopardize the Barack Obama administration's rebalance to Asia, which seeks to strengthen "minilateral" partnerships among Asian allies and partners. The ongoing, and in some areas worsening, tensions between Seoul and Tokyo constrain Washington's influence in East Asia by limiting joint contingency planning and trilateral coordination for crisis management as well as the ability to address the challenge of China's rise.
As North Korea expands its nuclear and missile capabilities and as China pushes to expand its influence in East Asia, often at the United States' expense, an increasing number of U.S. policy analysts are calling on the United States to shed its long-standing reluctance to intervene more forcefully in Japan-South Korean disputes despite the risks of doing so. U.S. policymakers have a number of options for facilitating closer bilateral cooperation between Tokyo and Seoul, as well as trilateral cooperation among Tokyo, Seoul, and Washington. Although more forceful intervention in Japan-South Korea relations carries risks to the United States, the costs of nonintervention are rising.