UNDERNEATH THE “TOWER of the Korean War”, a monument in Seoul resembling a bronze sword, is a bunker managed by the Ministry of Public Administration and Security. Inside, visitors learn how to protect themselves from a North Korean attack, chemical (seal the windows), biological (cover your mouth and nostrils) or nuclear (find a bunker). A squad of cadets, in the middle of their 21 months of mandatory military service, troop inside, don 3D glasses and watch a stirring televised account of the bombardment of Yeonpyeong island in November 2010 by North Korean artillery, which killed two soldiers and two civilians in the first shelling of South Korean territory since the end of the Korean war. The North Koreans, some analysts assumed, were trying to bolster their new general, Kim Jong Un, in preparation for his succession to the throne of the Kim dynasty.

After taking power on the death of his father, Kim Jong Il, in December 2011, the young Mr Kim set off another round of less deadly but more unsettling provocations. Last December his regime launched a satellite into space, beating the South Koreans by a month in their race to join the space club. In February it tested a nuclear device, North Korea’s third and most successful detonation. It promised to restart the plutonium reactor in Yongbyon, and it prevented South Korean workers crossing the border to their jobs at the Kaesong industrial complex, the only surviving joint economic initiative between the two countries. In March cyber-attacks, possibly from the north, debilitated the computer networks of three South Korean banks and three television stations. That was followed by histrionic threats to attack Guam, Okinawa, Hawaii and the American mainland itself. But even though Mr Kim comically overstates his strength, the rest of the world should not underestimate it. The North Koreans have “consistently outperformed the expectations of the outside world”, said Stephen Bosworth, a former American special representative for North Korea policy, at a Senate hearing earlier this year.

This outperformance was witnessed at first hand by Siegfried Hecker, a Stanford professor who once ran America’s Los Alamos National Laboratory. In November 2010 the North Koreans invited him to Yongbyon, the site of its plutonium nuclear reactor. They showed him a facility for enriching uranium which they said would serve a civilian purpose. Dr Hecker’s first look through the windows was “stunning”, he wrote. “We saw a modern, clean centrifuge plant of more than a thousand centrifuges all neatly aligned and plumbed below us.”

Another expert impressed by North Korea’s nuclear advances was Abdul Qadeer Khan, the godfather of Pakistan’s nuclear programme. He heaps scorn on Libya’s efforts but reserves praise for the North Koreans. They showed him the “perfect nuclear weapon”, he wrote, “technologically more advanced than ours”.

To develop a credible nuclear threat, a country has to accomplish four tasks: obtain the explosive or fissile material; incorporate the explosives into a warhead small enough to fit on a long-range missile; build a long-range missile; and secure a platform to launch it from. How far has North Korea got?

Take the tasks in reverse order. The launch platform would ideally be a stealthy submarine that could dispatch a nuclear missile even after North Korea itself had suffered a nuclear attack. North Korea’s submarines are not up to that task (although it has recently paraded a launcher that can move on land), so its launch facilities would probably not survive for long in an all-out conflict with America and South Korea. But that would give North Korea an incentive to use its nuclear weapons early if it is to use them at all.

Missiles have not only to go up but also to come down again

What about its missiles? In December North Korea launched a satellite using a three-stage rocket, the Unha-3, that would be capable of hitting the continental United States. It was a significant breakthrough. However, missiles, unlike satellites, have not only to go up but also to come down again. North Korea has not yet tested a vehicle that can make a controlled re-entry into the atmosphere and find a target.

To travel intercontinental distances, warheads must be miniaturised. According to David Albright of the Institute for Science and International Security (ISIS), it took Pakistan only ten years to miniaturise a warhead for its Ghauri missile, which was based on North Korea’s medium-range Nodong model. Since the North Koreans started on the same task at least 20 years ago, they have probably mastered it by now. The Nodong missile is capable of hitting Japan. Fitting a warhead to the longer-range Unha-3 is still several years off, Mr Albright reckons.

The core of the matter

Nuclear warheads require fissile material, either plutonium or highly enriched uranium. One way of getting hold of that is to import it. North Korea may, for example, have smuggled plutonium out of the former Soviet Union. Alternatively the fissile material can be made at home. One method is to burn natural uranium in a nuclear reactor to generate fissile plutonium. Another is to separate fissile uranium from the inert sort in a gas centrifuge. This highly enriched uranium can be used for making bombs without the bother of having a nuclear reactor.

North Korea has long experience of the first method. Its small Yongbyon reactor, which appears to have been restarted after a long pause, can make about one bomb’s worth of plutonium a year. From its past operations North Korea may also have stockpiled enough plutonium for anything from six to 18 weapons, according to a 2012 study by ISIS.

Enriching uranium is more difficult but more direct. Gas centrifuges of the kind that dazzled Mr Hecker are easier to hide than nuclear reactors, but they are tricky to build and operate. The United Nations had hoped to stall North Korea’s progress by preventing it from importing the necessary parts and materials, but two American analysts, Joshua Pollack, a consultant to the American government, and Scott Kemp, of the Massachusetts Institute of Technology, recently concluded that North Korea could now make much of the specialised equipment on its own.

Can the rest of the world stop North Korea getting any further? Probably not. America and South Korea have been trying to disarm it for two decades, using a variety of approaches, but with little success.

After power passed to the opposition in South Korea’s 1997 elections, the new president, Kim Dae-jung, experimented with a “sunshine” policy, hoping that promises of peace and reconciliation, together with dollops of aid, would persuade the north to shed its hostility. His successor, Roh Moo-hyun, continued that policy. By contrast, Lee Myung-bak, who was president from 2008 to 2013, adopted a notably tough stance, in the belief that the dictatorship was close to breakdown.

Distrustpolitik

The current president, Park Geun-hye, intends to use both carrots and sticks, rewarding the north for co-operating and punishing its provocations. She has called her approach “trustpolitik”, although “distrustpolitik” might be more apt. The south does not trust the north to keep its promises; the north does not trust the south to follow through on its admonitions.

The carrots could include a bit more aid, especially food aid and medicines. The south has already helped the north reopen the Kaesong industrial complex, a joint manufacturing hub near the border where North Korean labour combines with South Korean capital to make footwear, watches, garments and other light industrial products for export. For the north the complex is an important source of foreign exchange; for the south it is a symbol of inter-Korean co-operation.

The sticks include a sterner response to provocations such as the shelling of Yeonpyeong island. Although South Korea’s howitzers returned fire, their response was inhibited by fears of the fighting getting out of hand. The south’s armed forces are geared to defending itself or, if necessary, destroying the north. They are less well prepared to respond to the north’s pinpricks.

In pursuing the broader goal of disarmament, the only stick of substance remains sanctions. The United Nations embargo, backed by all the members of the Security Council including China, was tightened after the December satellite launch and again after the February nuclear test. It aims to ban trade in items the north might need for its weapons (such as gauges for wind tunnels), luxury goods its rulers might want for themselves (such as yachts, jewellery and racing cars) and also the foreign cash they would need to buy them.

But the sanctions remain porous. North Koreans have evaded financial curbs by couriering cash in bulk. When the UN blacklists a company, it just changes its name. Ships are renamed and reflagged. The North Koreans also convert civilian goods to military use. They once bought six off-road lorries for carrying timber and turned them into mobile missile launchers.

The trouble is that any sanctions weighty enough to stop the North Koreans realising their nuclear ambitions are unlikely to secure China’s support; conversely, any sanctions that China will support will not be enough to stop the North Koreans. This impasse reflects China’s equivocal relationship with its troublesome neighbour and North Korea’s unequivocal commitment to nuclear weapons.

By tradition, China has viewed North Korea as an ideological soulmate that can “stand sentry” against American forces stationed in South Korea, points out Ren Xiao of Fudan University. These assumptions still shape China’s dealings with the north. But some in China now say that far from providing a buffer against American influence, North Korea is a magnet for trouble, drawing America into the region. They conclude that China should abandon North Korea. Others suggest that China merely treat North Korea like any other state, helping it only when it shows respect for China’s own national interests.

In carrying out its latest missile and nuclear tests, North Korea clearly disregarded those interests. The third nuclear test even disrupted the Chinese New Year holidays, notes Mr Ren. The defiance was probably calculated, argues John Delury of Yonsei University in Seoul: North Korea’s new young leader had to show the “feisty guerrilla spirit” expected of North Korean rulers. But although his feistiness may have gone down well at home, it seems to have stuck in the craw of Xi Jinping, China’s leader. In June Mr Xi hosted a state visit from South Korea’s new president, who speaks decent Chinese and was keen to mend fences broken by her predecessor. The new warmth in their relationship was in palpable contrast to the frostiness in his dealings with the north.

China does not want a nuclear North Korea, not least because it might inspire South Korea and Japan to develop nuclear weapons of their own. But North Korea is so determined to pursue its nuclear ambitions that the Chinese would have to threaten the regime’s very existence before it abandoned them. China has the means to do so: it accounts for 70% of North Korea’s trade, runs many of its neighbour’s mines and hosts tens of thousands of North Korean workers, whose remittances are a vital source of foreign exchange. If the border were closed, the economic disruption would destabilise the regime. But that is precisely why China will not close the border. The one thing it wants even less than a nuclear north is an unstable one.

So if the regime survives, it is likely to realise its ambition for nuclear weapons. And its chances of survival seem to have improved lately. Mr Lee, the former South Korean president, pinned his expectations for North Korea’s collapse on economic failure and a botched leadership transition. But the economy has grown for the past two years, according to the south’s Bank of Korea, and exports have leapt by 90% over that period. Many North Korean children remain ill-fed: 5% still suffer from acute hunger and an appalling 32% from chronic undernutrition. But as Hazel Smith of Britain’s Cranfield University has pointed out, both these figures are much lower than in India and Indonesia, where nobody sees them as regime-changers.

Kim Jong Un also appears to have cemented his grip on power. North Korea’s political system requires “a man at the top to whom all issues are referred and from whom all wisdom flows,” said Glyn Davies, America’s special representative on North Korean policy, in testimony earlier this year. North Korea, Mr Delury points out, “is a survivor”. It is the oldest regime in East Asia, predating the People’s Republic of China by a year. Over its long life it has endured sanctions, famine and the collapse of a planned economy without succumbing.

If Kim Jong Un were to get his finger on a nuclear button, it would represent a dramatic defeat for more than two decades of international diplomacy. It would damage the credibility of America’s efforts to prevent other countries, such as Iran, arming themselves with nuclear weapons, and it would make a mockery of a string of solemn resolutions of the United Nations Security Council.

But despite all this diplomatic anguish, a fully fledged North Korean nuclear arsenal would not make much difference to the national security of either North or South Korea. Mr Kim’s dictatorship can already inflict enough damage on Seoul to deter any outside attempt to topple his regime. Likewise, South Korea, with the help of its American ally, can already deter a North Korean invasion, even if North Korea develops a more “perfect” nuclear weapon.

The damage that even a primitive weapon could inflict on South Korea does not bear thinking about, but some analysts are paid to do just that. Bruce Bennett of the RAND Corporation, a think-tank, has tried to quantify the horror of a ten-kiloton warhead exploding in Seoul. Such a weapon is not hard to make; the Americans built a bigger bomb 68 years ago. Yet it would still kill 125,000-235,000 people, Mr Bennett calculates. A similar number would suffer from radiation sickness, terrible burns and other injuries.

Enough already

And North Korea’s nuclear weapons are not the only threat it can muster. American generals trot out a grisly list of chemical and biological weapons at the regime’s disposal, spanning much of the alphabet: anthrax, botulism, cholera, haemorrhagic fever, nerve agents, plague, smallpox, typhoid and yellow fever. “Even a limited attack with these systems could cripple the…economy and panic the populace,” noted General James Thurman, who commands the combined American and South Korean forces, in testimony to Congress in 2012. His forces in Seoul are trying to defend one of the world’s great metropolises, a highly evolved, tightly knit miracle of human endeavour, ingenuity and co-ordination. It would not take much to throw such an elaborate organism into chaos.

The forces arrayed against North Korea are even more formidable: 639,000 South Korean troops, 5,300 artillery pieces and 460 combat aircraft, buttressed by over 28,000 American troops and a nuclear guarantee from the world’s only superpower. Thanks to this concentration of arms, the Korean peninsula is already locked in a military stalemate that nuclear weapons would only reconfirm.

So North Korea’s regime looks likely to survive for the foreseeable future. That will inspire mixed emotions among many South Koreans. To them, the demise of the North Korean regime and the reunification that might follow is an abstract hope mixed with concrete fears. Only about 5% of South Korea’s population has any memory of an undivided Korea, and a diminishing number has relatives in the north. The latest survey of public attitudes by the Asan Institute, a think-tank financed by Hyundai, shows that only 32% of all South Koreans, and only 18% of people in their 20s, still see North Korea as “one of us”. South Koreans would be glad to see the back of the Kim dynasty, but they are not keen to shoulder the burdens it will leave behind. They have plenty of problems of their own.