President Obama correctly decided—apparently after some deliberation—to include South Korea on the itinerary for his trip to Asia in April, thus avoiding straining relations with a key ally. Seoul and Tokyo are again embroiled in a flare-up of tensions over sensitive historical issues that risk undermining U.S. security interests in Asia. Had Obama traveled only to Japan, as originally planned, South Korea would have interpreted it as the U.S. condoning Prime Minister Shinzo Abe’s flawed revisionist interpretation of Japan’s wartime actions.

Now that diplomatic niceties have been preserved, the United States needs to prepare a new approach to its two treasured but recalcitrant allies. There is a growing consensus in Washington that the U.S. needs to take a more active role in ameliorating the tensions between Seoul and Tokyo. There is less agreement, however, on the precise role that Washington should take.

The U.S. remains wary of assuming a mediator role given the dangers of being perceived as taking sides on issues that inflame fervent emotions in both South Korea and Japan. There also seems little incentive to become deeply involved when both allies resist entreaties to moderate their behavior.

Haunted by History

Japan feels it has shown sufficient contrition for its wartime past, citing a long list of apologies and the passage of time. Japan’s neighbors, particularly South Korea and China, question the form and sincerity of those apologies. Japanese efforts are thwarted when officials reopen still unhealed wounds through offensive remarks.

Abe’s visit in December 2013 to the controversial Yasukuni Shrine showed either defiance or severe misjudgment of Washington’s reaction. Japanese media expressed shock and outrage at the U.S. government’s public mild expression of “disappointment.” Yet the reality was that the U.S. was privately seething at Abe’s action. Washington’s ire was exacerbated by public Japanese ruminations questioning the reliability of the U.S. defense of Japan.

Across the Sea of Japan—or the East Sea, as Korean activists would have U.S. textbooks define it—the Park Geun-hye administration has also disappointed Washington by resisting compartmentalizing its foreign policy, instead allowing the ghosts of the past to haunt present-day policymaking. South Korean polls show that the public and policymakers are more worried about the hypothetical resurrection of a threat from the last century than confronting the very real threats of today.

The depth of South Korean resentment is embodied in the controversy over South Korea’s military accepting 10,000 bullets from Japan. South Korean peacekeeping forces in Sudan faced imminent threat and called for more ammunition. The only other United Nations force with the same caliber bullets was Japan, which provided the requested assistance. Yet the ensuing public uproar in South Korea forced the return of the bullets. Apparently South Korea would rather see its own troops placed at risk than show the slightest sign of reconciliation with Japan.

Similarly, South Korean Minister of Foreign Affairs Yun Byung-se stated in early February that Seoul should consider forging a military intelligence-sharing agreement with China. If Seoul were to do so before finalizing a similar agreement with fellow democracy Japan, it would show how skewed South Korean foreign policy priorities have become. Such an agreement would also raise U.S. concerns over the military and intelligence information shared with its South Korean ally.

China and North Korea both pose security threats to South Korea, while Japan does not. Beijing pursues an aggressive foreign policy of bullying and intimidation fueled by massive increases in defense spending. Beijing has repeatedly obstructed international efforts to curtail North Korean violations of U.N. resolutions and respond to Pyongyang’s two deadly attacks on South Korea in 2010.

South Korea canceled senior-level meetings with Japan but recently accepted North Korea’s offer for talks. South Korea is more willing to pursue a trustpolitik policy of mutual trust-building efforts with Pyongyang—which killed 50 South Koreans in 2010 and continues to threaten South Korea with nuclear annihilation—while refusing to engage with Tokyo.

What the U.S. Should Do

Private U.S. messages of increasingly stronger tone failed to deter Abe from visiting the Yasakuni Shrine. Abe’s trip destroyed nascent efforts to repair relations with Seoul and risks derailing his efforts to implement long overdue, pragmatic revisions to Japan’s defense posture. Washington’s long-standing efforts to have Japan assume a larger role for its own defense and to address international security threats have been jeopardized.

Washington now needs to press Tokyo to begin a reconciliation process with Seoul for resolving divisive historical issues. This process should include, at a minimum, an unequivocal public affirmation of the Kono and Murayama statements of contrition; a mutually agreed upon mechanism for compensating surviving women forced into sexual slavery during World War II; and a pledge by the prime minister not to visit the controversial Yasukuni Shrine again. For its part of the process, Korea should acknowledge the progress and reciprocate by agreeing to a bilateral leaders’ summit.

The Obama Administration should make clear to Tokyo that it will publicly rebuke and condemn reprehensible revisionist comments by Japanese officials, such as those recently proclaimed by government-appointed governors of the Japanese NHK broadcasting network.

Similarly, Obama should use his trip to urge Seoul to compartmentalize and prioritize its foreign policy. A myopic focus on history works against all three countries’ national interests in light of rising present-day security threats. The President should also reassure Seoul that reforms to Japan’s minimalist security stance, such as exercising collective self-defense, is not a security threat to Japan’s neighbors.

Seoul should sign the bilateral South Korea–Japan General Security of Military Information Agreement. Seoul’s refusal to do so as planned in 2012 and to join the comprehensive allied missile defense network increases the risk to the Korean populace from North Korean missiles equipped with nuclear, chemical, and biological warheads.

Washington should recommend creation of a Trilateral Security Initiative of their foreign and defense ministers to develop joint strategies for addressing common threats and objectives, responding to North Korean provocations, and a strategy for Korean unification, including aid and development contributions.

The allies should resume bilateral South Korea–Japan and trilateral South Korea–Japan–U.S. military exercises and maritime security. The three countries should explore the potential for joint peacekeeping missions, counterterrorism, counter-proliferation, counter-narcotics, anti-submarine warfare, mine-sweeping, cyberspace protection, and humanitarian assistance and disaster response operations.

Circular Firing Squad

Without U.S. shuttle diplomacy between its allies, Japan and South Korea will remain fixated on the past to the detriment of the future. The three countries are reliant on each other for ensuring the region’s security. Continued tensions among the U.S., Japan, and South Korea could degrade allied responses to a range of regional security crises.

—Bruce Klingner is Senior Research Fellow for Northeast Asia in the Asian Studies Center at The Heritage Foundation.