Surrounded by a nuclear-armed Russia, China and North Korea, South Koreans live in a threatening neighborhood. Their government’s first goal should be to lessen the risks they face. By withdrawing from a three-year-old military information pact with Japan, the administration of President Moon Jae-in has done just the opposite.

The General Security of Military Information Agreement allowed the two U.S. allies to share sensitive intelligence directly and swiftly, without having to go through Washington. Losing the channel will make it harder for their militaries to monitor North Korea’s nuclear and missile programs — and, no less important, harder for the U.S. to coordinate a response in the event of a crisis. South Korea’s decision appears to have surprised and angered American officials.

Japan is partly to blame. This latest feud between the two countries began after a South Korean court awarded damages to Korean workers forcibly conscripted by Japanese companies during World War II — an issue Japan insists was settled when the two countries reestablished diplomatic relations in 1965. Frustrated by Seoul’s refusal to put the question to arbitration, Prime Minister Shinzo Abe’s government tightened Japan’s controls over exports of sensitive materials to South Korea. Bringing trade weapons to bear in a political dispute was wrong in principle and foolish as a practical matter. It aroused public anger in South Korea, virtually guaranteeing that Moon would have to respond in kind, and it invited escalation.

That said, South Korea should have resisted the invitation. Having imposed similar limits over exports to Japan, it could have left it at that. Moon won plaudits for saying on Aug. 15 that Korea was open to talks. By scrapping the intel-sharing pact a week later, he made that more difficult. Moreover, South Korea is the main loser. Japan has military satellites and anti-submarine capabilities that South Korea lacks, and these will be crucial as the North develops its arsenal of sea-launched ballistic missiles. In a region where Seoul needs every friend, Moon has made military cooperation with Tokyo far more difficult.

He has also damaged South Korea’s most vital relationship: its alliance with the U.S. The move ignores clear advice from Washington, and potentially endangers the 80,000 American troops stationed in Northeast Asia. The new tension strengthens both China and Russia, whose joint military activities in the region have been growing bolder. U.S. President Donald Trump had already expressed reservations about stationing American forces on the Korean Peninsula. Moon hasn’t helped on that score.

South Korea needs to reverse this decision before the pact expires in three months. Japan can help by opening talks to resolve the dispute over export controls. If those concerns are separate from the forced-labor question, as Japanese officials say, they can be resolved. But steps toward settling the historical claims are needed, too. Japan’s call for third-party arbitration is both legally sound — the 1965 normalization agreement provides for it — and politically astute. A compromise will be possible only if this issue is removed from the public arena.

The U.S. should already have intervened more forcefully. Although no compromise imposed from outside is likely to last, diplomatic pressure from Washington would at least help to get the principals talking. Let this foolish and dangerous feud drag on, and it will only get worse.