Joe Biden wasted no time in affirming American security assurances to South Korea’s President Park Geun-hye during his meeting in Seoul, stating that it has “never been a good bet to bet against America . . . and America will continue to place its bet on South Korea.”

The words were not new, but they were no doubt welcome in Seoul, given that South Korea suddenly finds itself directly affected by dual regional security crises from both an internally fluid North Korean leadership situation and from South Korea’s southern maritime flank following China’s unilateral assertion of an Air Defense Identification Zone (ADIZ) on November 23. The Chinese declared zone overlaps with South Korea’s own zone and intersects with South Korean maritime claims that are outside of South Korea’s proclaimed ADIZ. South Korea had previously viewed East China Sea disputes between China and Japan as a bilateral problem that did not affect South Korean security interests, but China’s ADIZ assertions have drawn South Korea into the dispute as a concerned party for the first time, creating a situation in which South Korea feels security threats from all sides. A strengthened U.S.-ROK security commitment provides the only viable antidote to this situation.

Moreover, China’s ADIZ declaration has set back positive momentum in China-South Korea relations. China’s announcement caught South Korea short because South Korea’s declared ADIZ does not cover its existing territorial and maritime claims. South Korea’s unilateral declaration of its own expanded ADIZ is viewed as a necessary corrective in Seoul, but it might run the risk of further escalation, compounding China’s unilateralist mistake. South Korea’s announcement of an expanded ADIZ would both increase the area of conflicting Chinese and South Korean air zones and bring South Korea’s zone into conflict with Japan’s ADIZ. It would also run the risk of inducing additional ADIZ claims by China on South Korea’s west and by Japan on South Korea’s east. Any South Korean declaration of an expanded ADIZ will benefit from being informed by prior conversations on the issue in Tokyo and Beijing.

South Korea’s ADIZ dilemma exposes the dangers that accompany the current disconnect in Japan-ROK relations on three counts: 1) effective South Korean bureaucratic coordination with Japan is necessary to manage issues such as the declaration of a new ADIZ that overlaps with that of Japan, 2) poor management of Japan-ROK relations weakens the U.S.-led alliance network that underpins the Obama administration’s rebalancing strategy, and 3) South Korea and Japan have differing diplomatic strategies toward and relationships with China, making the prospect of a fully coordinated U.S.-Japan-ROK approach toward China unlikely for now.

Park’s reported response to this message from Vice President Biden was more diplomatically phrased than her emotional statements on Japan to Secretary of Defense Hagel in early October, which set off alarm bells in Washington. But they still squarely communicated the expectation that the ball is in Japan’s court to take the first steps to address historical issues that prevent the improvement of Japan-ROK relations. Unless Park and Abe can muster the statesmanship to frame a win-win political formula for addressing the issues that divide their two countries, all bets are off; the fraught South Korea-Japan relationship may remain the Achilles’ heel of the U.S. rebalance that Biden so energetically championed in Seoul.