POSTERS showing rockets raining down on Washington, DC; YouTube videos of Manhattan going up in smoke and Barack Obama engulfed in flames: the world is used to North Korean threats of nuclear apocalypse. But its chest-thumping in recent weeks has been unusually martial. After the UN tightened sanctions on the regime following its third nuclear test in February, Kim Jong Un, the country’s young dictator, declared a new state of war with South Korea, advising foreigners to evacuate before the looming “thermonuclear” conflict. How scared should the world be of North Korea's nukes? North Korea has dabbled in nuclear technology since the 1960s, when it built a research centre in Yongbyon, now its main nuclear facility. Although the two Koreas agreed to a nuclear-free peninsula in 1992, the North pulled out a year later. This month it announced the reopening of a nuclear reactor at Yongbyon, which produced plutonium until it was shut down in 2007 as part of a foreign-aid deal. But it will probably be two to three years before the reactor produces any new plutonium. That said, North Korea may have enough weapons-grade plutonium stockpiled to make a handful of warheads. But even though the bomb detonated in February is thought to be smaller, lighter and more powerful than the previous two tested, it is probably too large to mount on North Korea's rockets. Those rockets are, in turn, unreliable and inaccurate: it took the regime 20 years after the launch of its first short-range missile to develop the long-range rocket (Unha-3), which successfully put a satellite into orbit in December 2012. Despite propaganda to the contrary, North Korea could not deliver a nuclear warhead to the American mainland. And its warning of “thermonuclear war” rings hollow because it has no hydrogen bombs.

In short, North Korea’s threatening rhetoric exaggerates its capacity to wreak nuclear havoc. But its nuclear programme is still worrying for other reasons. The technical deficiencies in its warheads and missiles could be overcome, given enough time (though American missile defences, like those being sent to Guam, will also improve). If its most recent bomb turns out to have used uranium rather than plutonium, the North could ramp up production far more quickly: the country has plenty of uranium-ore deposits and enrichment is easier to conceal. The most immediate danger is that North Korea sells its know-how and material to other rogue states, such as Iran (which also uses uranium), or to terrorists unconcerned about accuracy. A further proliferation risk is that as North Korea's technology improves, Japan and South Korea may be encouraged to start weapons programmes of their own.

At the moment a conventional conflict, triggered by accident, poses the greatest risk. Although North Korea's newest rocket has never been tested as a missile, its suspected range of 6,200 miles (10,000km) would be enough to reach America's west coast. North Korea has about 200 shorter-range missiles that could hit American bases in Japan and South Korea, and another 600 that could strike Seoul. It also has 1.1m soldiers, three-quarters of them stationed within 60 miles (100km) of the demilitarised zone between the two Koreas, and 10,000 artillery pieces pointing towards Seoul. For years, engagement with North Korea has been on the basis that it would give up its nuclear ambitions in return for aid. It now says its nuclear programme is non-negotiable. The scariest thing about North Korea's nukes is that it no longer considers them as bargaining chips, but as weapons.

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