The months-old dispute between the two countries is only growing. They may not be the only ones affected

Perhaps the most striking aspect of the row between Japan and South Korea is that it is not in the interests of either side, yet continues to escalate. The rest of us should also pay attention because the repercussions could be felt much further afield.

Simmering bitterness over the Japanese occupation from 1910 to 1945 bubbled up again with a row over the issue of the South Korean women who became “comfort women” (wartime sex slaves), and then last year’s ruling by the South Korean supreme court that workers were entitled to compensation from Japanese firms for their forced labour during the war. Tokyo sees Seoul as reneging on a 1965 bilateral agreement settling wartime claims; Seoul believes that Tokyo has not done enough to address its colonial past and says the deal should not prevent individual victims from suing.

Then, in July, Japan put sanctions on chemicals essential to South Korea’s electronics industry, before removing it from its “whitelist” of trading partners. This week, South Korea took Japan off its own list. The removals essentially make trade between two closely intertwined economies less convenient. But Seoul’s decision to scrap an intelligence-sharing pact is much more concerning, and a South Korean consumer boycott has hit everything from car and beer sales to tourism and films. A deeply emotional dispute is having material consequences.

Seoul’s Moon Jae-in faces a flagging economy, discontent over stalled attempts to improve ties with North Korea, and corruption allegations involving his justice minister – damaging for an administration that sold itself as a clean alternative to its predecessor. As deeply felt as the historical grievances are, the current row looks rather like a welcome distraction. Japan’s Shinzo Abe is a rightwing revisionist who sees its postwar culture of contrition as masochistic.

But the costs of a trade spat between the world’s third and 11th largest economies, particularly given the Sino-US trade war and slowing global growth, are obvious. It is hardly ideal for neighbours of a nuclear North Korea to have begun squabbling, nor for two Asian powers with so many shared interests to be diverging when others are likely to exploit the tensions. Russia and China carried out their first joint air patrol in the region in July, prompting both Seoul and Tokyo to scramble aircraft.

Since such issues interest the US too, it has often mediated between its allies. But Mr Trump takes a transactional approach to international relations, and guns for flashy and unlikely diplomatic wins; he has no interest in quiet intercession. His administration is less capable of such work than its predecessors. Issues such as Iran and Afghanistan are pressing. It is not clear that anyone else has the ability or inclination to act in place of the US, though the EU should try. But US failings make the relationship between Japan and South Korea all the more important. If they do not find ways to work together again, others will pay too.