The second meeting between the leaders of the United States and North Korea in Hanoi earlier this year challenged the conventional wisdom that there is no such thing as a failed summit when it ended without any agreement being signed. The widespread consensus is that the Trump administration was responsible for the breakdown of the talks.

For the Japanese government, though, the outcome was acceptable, given that the Trump administration, which had been taking advantage of joint projects between North and South Korea to proactively negotiate with Pyongyang, halted the talks calmly.

While this was a setback for North Korean leader Kim Jong Un, the hardest blow was to the government of South Korean President Moon Jae-in. Just before the summit, Moon shared his vision for a proposed “new Korean Peninsula regime” designed to kick-start economic cooperation between North and South by resuming tourism at Mount Kumgang and operations in the Kaesong Industrial Region. That vision was derailed.

South Korea must step up its intermediary role between the U.S. and North Korea. This will not be easy now that the yawning gap between Washington and Pyongyang has been exposed. Can the Moon administration effectively balance relations with the U.S. and North Korea? In fact, the U.S.-South Korea summit on April 12 ended in failure because Moon could not persuade U.S. President Donald Trump to ease the sanctions against North Korea.

Meanwhile, some observers are laying the blame for the failure of the talks at Japan’s feet, as shown by statements emerging from South Korean government circles that Tokyo wanted the negotiations to break down and used its influence to achieve that outcome. Similar criticisms have emerged from North Korea.

There is no doubt that the Japanese government lobbied not only the Trump administration but also the diplomatic establishment in Washington, so that Trump would not go too far in compromising with North Korea. Really, it is hardly surprising that the Trump administration would ensure that its impatience for success did not harm the interests of its ally Japan.

However, if North Korea’s denuclearization project is to succeed, the South Korean government should not slacken in its efforts to obtain support, emphasizing the fact that the project would benefit both the U.S. diplomatic establishment, including the Democratic Party, and Japan. This is not easy, but without this effort it is clear that South Korea will not be able to realize its vision.

However, the Moon administration has struggled in this regard. In Washington, the thinking is that it is doubtful that the denuclearization of North Korea can be achieved through the Moon administration’s policy of appeasement. Meanwhile, a series of historical grievances, including the issue of “comfort women” and that of conscripted wartime workers, has had an adverse impact on relations with Japan, which has now lost all trust in the South Korean government.

The argument that Japan was behind the breakdown of the Hanoi talks overstates Tokyo’s diplomatic clout. Ever if it were true, then one must ask why South Korea didn’t make the effort to win Japanese support first, at the very least by maintaining good relations. The thinking that Japan does not want Korean unity is misplaced: Tokyo is not opposed to South Korea-led unification. Rather than misguided assumptions, South Korea should be working to win Japanese support by highlighting the benefits of unification.

To be clear, the Moon administration’s efforts should be applauded. They will have a positive impact on the security of Japan, the Korean Peninsula and Northeast Asia. If the scenario envisioned by South Korea becomes reality, it would be all for the better.

However, the state of relations between South Korea and Japan remains a significant impediment that will require some serious diplomacy to overcome.

South Korea has its own domestic politics to consider, and so compromise with Japan on historical issues will always be difficult. However, the current policy in Seoul seems to suggest no forward movement at all. Of course, this can’t be attributed entirely to the Moon government; in the current climate it is difficult for Japan to be proactive as well. Still, given the importance of North Korean denuclearization for Japan’s security, the rational choice for Tokyo is to let go of its distrust and work with Seoul to achieve that outcome.

Tadashi Kimiya is a professor at the University of Tokyo. ©2019, The Diplomat; distributed by Tribune Content Agency, LLC