Finally, it looks like Japan-South Korean relations are on the mend, though the two governments have certainly given skeptics reason to believe that irreparable damage has been done. As a former trilateral coordinator with those countries, I remain one of the more optimistic of the bunch, owing to my understanding of a few key principles that underwrite the relationship.

There are still miles to go before the two governments can get things back on track, but there remains an actionable foundation for long-term cooperation provided two things happen: Prime Minister Shinzo Abe and South Korean President Moon Jae-in have to take advantage of open doors to cooperation, and the U.S. government must continue opening some of those doors.

For nearly two years, we've seen report after report on the degrading ties between the Japanese and South Korean governments. In November 2017, South Korean Foreign Minister Kang Kyung-wha announced that the Moon administration was pulling back from the 2015 "comfort women" agreement, which was supposed to resolve the issue at the intergovernmental level.