OBSERVERS OF MILITARY developments on the Korean peninsula were given whiplash on September 15th. Around lunchtime in Seoul, news broke that North Korea had fired two ballistic missiles off its east coast. Shortly afterwards the South Korean government announced that Moon Jae-in, the president, had observed the successful test of a submarine-launched ballistic missile, the development of which the armed forces had previously declined to confirm. The parallel tests came hot on the heels of reports from North Korean state media that the country had successfully tested a new class of cruise missile over the weekend. For good measure, South Korea confirmed this week that it had recently developed a new cruise missile, too.

The tests highlight an accelerating arms race on the peninsula. North Korea, which refrained from testing missiles during a period of detente with South Korea and America in 2018 before resuming testing in 2019, has since continued to expand both its nuclear and its conventional arsenal, in the face of UN sanctions that ban it from developing nuclear weapons and ballistic missiles. It has focused in particular on new missiles that may be better at evading the South’s detection systems, rather than inter-continental ballistic missiles of the sort that could threaten America. Meanwhile the South has been ramping up defence spending and beefing up its own arsenal.

Building ever more fearsome weapons has been North Korean policy for decades. Kim Jong Un, the current dictator, sees it as essential to his survival, as did his father and grandfather before him. The South’s build-up has accelerated more recently, driven by growing concerns about the durability of the alliance with America, and shifting dynamics in the region given increasing tensions between China and America. Donald Trump, America’s previous president, fuelled those concerns with his isolationist rhetoric and his view of alliances as expensive favours to free-riding foreigners. So did the perceived lack of support from America when South Korea suffered a painful Chinese boycott after agreeing to the deployment on its soil of an American anti-missile system in 2017. Since taking office that year, Mr Moon has worked to make South Korea less dependent on America for its defence. He has pushed for the transfer of wartime command of troops on the peninsula from American generals to Korean ones and has tried to build closer ties with allies in South-East Asia.

Diplomatic efforts to defuse tensions on the peninsula have been deadlocked since a brief thaw in 2018 and 2019. North Korea has spent the best part of two years entirely closed off from the world in a bid to ward off covid-19. The restoration of a communications link between the two Koreas in June (following the demolition of a joint liaison office by the North a year earlier) did not lead to a wider detente. Then the North stopped returning the South’s calls ahead of joint military exercises between the South and America in mid-August.

The exercises, which the North views as practice for an invasion by the South, may be one reason it has resumed testing, reckons Ramon Pacheco Pardo of King’s College in London. “They need to test those new missiles to see if they work, and doing it now allows them to send a message of disapproval at the same time,” he says. There is growing disillusionment about the prospect of further talks. The ballistic-missile tests came a day after Sung Kim, America’s special representative for North Korea, met senior South Korean and Japanese officials in Tokyo to discuss ways to persuade the North back to the table. South Korea’s armed forces, which after past tests had tended to be cagey about identifying the North’s weapons to avoid raising tensions, wasted no time on this occasion in noting that they were sanctions-busting ballistic missiles.

The timing of the South’s test, too, is hardly diplomatic. The submarine launch coincided with a visit to Seoul by China’s foreign minister, who had met his South Korean counterpart as well as Mr Moon earlier in the day. He was there to discuss not just relations between China and South Korea, but also joint efforts to persuade the North to resume negotiations about its nuclear arsenal. Mr Moon’s speech about the need for missiles on subs to defend against “omnidirectional threats” will not have helped with that. Meanwhile, South Korea’s National Security Council expressed “deep concern” about the North’s “provocation”. As a South Korean saying has it, “What I do is romance; what others do, adultery.”