No one wants to fight a nuclear war. Not in North Korea, not in South Korea and not in the United States. And yet leaders in all three countries know that such a war may yet come – if not by choice then by mistake.

The world survived tense moments on the Korean Peninsula in 1969, 1994 and 2010. Each time, the parties walked to the edge of danger, peered into the abyss, then stepped back. But what if one of them stumbled, slipped over the edge and, grasping for life, dragged the others down into the darkness?

This is how that might happen, based on public statements, intelligence reports and blast-zone maps.

March 2019: This time, the North Koreans went too far.

For years, North Korea had staged provocations – and South Korea had lived with them. The two had come close to war before: in 2010, a North Korean torpedo detonated just below a South Korean navy corvette, cutting the ship in two and sending 46 sailors to their deaths. Later that year, when North Korean artillery barraged a South Korean island and killed four more people, South Korean President Lee Myung-bak reportedly ordered aircraft to deliver a counter-strike deep inside North Korea, but the US military held him back.

This time was different. No one thought President Moon Jae-in, a progressive known for his attempts to engage North Korea, would want blood. But nobody grasped how quickly accidental violence could take on its own, urgent logic.

In late February, the United States was moving military forces into the region for an annual joint exercise with the South code-named “Foal Eagle”. South Korea had cancelled the 2018 exercise to avoid upsetting the North before the Winter Olympics in PyeongChang. To make up for the lost year, the 2019 drill was larger than ever.

When a South Korean airliner crossed over into North Korean airspace, a Northern air defence crew, already jumpy and anticipating the allied maneouvres in the Sea of Japan, mistook it for an American bomber. The crew fired a surface-to-air missile, sending the plane plunging into the ocean, killing all 250 people on board.

Kim Jong-un was referred to as ‘little rocket man’ in a tweet by Donald Trump (Getty) (ED JONES/AFP/Getty Images)

The South Korean public was outraged. Within hours, Moon ordered South Korean missile units to strike the air defence battery, as well as select leadership targets throughout North Korea. Moon’s limited missile strike might have been enough by itself to start the nuclear war of 2019. South Korean and American officials are still trading accusations. But the surviving members of the Moon administration insist that things would have been fine had President Donald Trump not picked up his smartphone: “LITTLE ROCKET MAN WON’T BE AROUND MUCH LONGER!”

It was an idle Twitter threat – Trump hadn’t yet been briefed about the missile strike, and it hadn’t yet been discussed on Fox & Friends. But how would Kim Jong-un know that? To him, with US forces lurking nearby and South Korean missiles slamming into his military sites, the meaning of Trump’s tweet seemed clear: Trump was now using the shootdown as a pretext for the invasion he had wanted all along.

Kim’s grandfather, Kim Il-sung, had begun North Korea’s nuclear weapons programme decades before. He had concluded, according to defectors who testified before the US Congress, that Saddam Hussein had made a terrible mistake in 1991 to sit back and watch the United States build up a massive invasion force. His son and grandson had watched Hussein dragged out of a spider hole and later hanged following the 2003 US invasion of Iraq. They had seen videos of Muammar Gaddafi’s gruesome death in Libya at the hands of rebels supported by US air power.

Each had made up his mind that, as soon as the United States moved to remove the Kim family from power, he would order the strategic rocket force of the Korean People’s Army to fire nuclear-armed short- and medium-range missiles at US forces throughout South Korea and Japan. Kim Jong-un hoped that the sudden attack would inflict tens of thousands of casualties, blunting the invasion force and stunning a casualty-averse American public. It was a desperate gamble, but doing nothing meant certain death.

And so, facing what he believed was a massive American military invasion, Kim gave the order. The thread of history winds along on twists of fate, like Archduke Ferdinand’s driver missing a turn.

For years, North Korean missile units had rehearsed this very scenario, taking Scud and Nodong missiles into the field at night to practice firing them against US forces in South Korea and Japan – using nuclear weapons to slaughter the enemy’s troops as they slept in their barracks or as they arrived at ports and airfields.

This time it wasn’t an exercise. In 2017, the US intelligence community had assessed that North Korea had as many as 60 nuclear warheads and was adding about 12 a year. That number was a little high: Kim did not have 72 nuclear weapons. But he did have 48.

The strategic rocket forces used 36 of them in the first wave. These missiles were largely extended-range Scuds and longer-range Rodongs. The launches looked exactly like the military exercises that the North Koreans had publicised year after year.

The targets in South Korea and Japan were largely located in urban areas. Yongsan Garrison, for example, was in the heart of Seoul. The Port of Busan, another important target, was in South Korea’s second-largest city. In Japan, many US bases were concentrated in and around metropolitan Tokyo – Yokota and Atsugi air bases, Yokosuka naval base. Marine Corps Air Station Iwakuni, about 20 miles from Hiroshima, was also targeted.

Some of these missiles broke up in flight, failing to reach their targets. US officials would later claim that they were intercepted by American and South Korean missile defences – although most experts dispute that. Observers had long warned that the effectiveness of missile defence was being exaggerated. Trump had told reporters in 2017 that Japan and South Korea could “easily shoot [North Korean missiles] out of the sky, just like we shot something out of the sky the other day in Saudi Arabia, as you saw”. In fact, Saudi and US officials knew that the defence had failed to intercept that warhead, which narrowly missed hitting an airport.

Many North Korean missiles did miss their targets in South Korea and Japan by a few kilometres. But these were fission devices, with yields similar to the nuclear weapons that destroyed Hiroshima and Nagasaki, and the bombs that fell off target still inflicted massive damage on urban areas. The blasts levelled buildings and were followed by massive firestorms that consumed large areas of Seoul, Busan and Tokyo.

For at least a few hours, the North Koreans were able to follow the nuclear attack with waves of conventional missiles and long-range artillery. People would remark on the heroism of the surviving firefighters trying desperately to extinguish the flames as missiles, some armed with chemical weapons, continued to rain down on them. The suffering would play out over many days, as survivors, afflicted with acute radiation sickness, picked their way through the rubble to die at home. As it had been in Hiroshima and Nagasaki in 1945, the infrastructure to provide medical care was overwhelmed.

Donald Trump’s use of social media has inflamed tensions between the US and North Korea (Getty)

North Korea fired a small number of its newer-generation Hwasong-12 missiles, also armed with nuclear weapons, at Okinawa and Guam. But at these ranges, the missiles are quite inaccurate – only about half fall within a few miles of their targets. All of the missiles aimed at Okinawa and Guam dropped into the ocean. A few people were killed in the panic and car crashes that followed the blinding flashes of the atmospheric nuclear explosions, but US military operations out of Kadena Air Base and Andersen Air Force Base continued.

Kim did not, on that first evening, use nuclear weapons against the US homeland. His strategy had been to halt the invasion and shock Trump. He knew he had 12 longer-range missiles in reserve, massive intercontinental ballistic missiles like the Hwasong-15 that North Korea began testing in late 2017 and that could deliver the North’s powerful new thermonuclear weapons. If Trump continued to threaten Kim’s hold on power, or if he and his family were to die at the hands of the Americans, Kim was determined to use these missiles to strike the United States mainland. He hoped the threat would cause Trump to come to his senses.

But Kim had misread the American mood. With airfields in Okinawa and Guam still working, and long-range bombers perfectly capable of striking North Korea from domestic bases, the United States mounted a massive air operation to kill Kim and destroy any remaining ballistic missiles that could be found. This campaign was, to the surprise of many observers, a conventional air campaign – US officials had concluded that the use of nuclear weapons would undermine the message that the United States was attempting to liberate the people of North Korea. Of course, Kim didn’t know that: Ongoing US air strikes left him almost completely cut off from communication with his military units, and in the fog of war, rumours about American nuclear strikes spread.

So Kim gave the order to use the remaining nuclear-armed Hwasong-14 and Hwasong-15 ICBMs against targets in the United States – two each against naval bases in Pearl Harbour and San Diego, along with leadership targets in New York, Washington DC, and – in a personal touch – a single missile aimed at Mar-a-Lago in Palm Beach, Florida, to bring the total to a dozen. The targets looked very much like the ones shown on a large map of the United States erected in Kim’s office, in front of which he had authorised the development of a nuclear strike plan in 2013.

The United States, of course, had a missile defence system in Alaska, along with a small number of interceptors in California. But the system was sized to deal with only 11 missiles. As it was, two-thirds of the North Korean missiles reached their targets.

The US Missile Defence Agency would later say this was a sign that the system had worked well, downing about a third of the missiles – although experts would argue that the low intercept rate resulted from problems that the Los Angeles Times had reported in 2017. The exoatmospheric kill vehicles had faulty divert thrusters, analysts said, making it unlikely that any had successfully intercepted incoming warheads. It seemed more likely, the experts said, that four of the missiles had simply broken up as they re-entered the earth’s atmosphere.

The remaining seven nuclear warheads landed in the United States. These missiles were no more accurate than the others – but with 200-kiloton warheads, 10 times the power of the bomb that destroyed Hiroshima, close was enough to count in most cases. Pearl Harbour took a direct hit with a single weapon, while San Diego was lucky: Both of the missiles aimed there failed to arrive.

One warhead hit Manhattan – which North Korea’s state media had specifically mentioned as a target of its long-range missiles – while the two missiles pointed at Washington struck the Northern Virginia suburbs. Trump, in a makeshift bunker in the basement at Mar-a-Lago, felt the earth shudder as the last warhead landed in the town of Jupiter, Florida, about 20 miles away. The other two missiles fell wildly off course, detonating in the ocean or in rural, sparsely populated areas.

In the next few hours, Trump was informed that allied air strikes had killed Kim. This was erroneous, but North Korea’s government had collapsed. Later, as US and South Korean forces combed through the Pyongyang suburbs, they would find Kim in a bunker, dead by his own hand.

The direct hit on Manhattan killed more than one million people. An additional 300,000 perished near Washington. The strikes on Jupiter and Pearl Harbour each killed 20,000 to 30,000. These were just estimates; the scale of the destruction defied authorities’ ability to account for the dead. Hundreds of thousands perished in South Korea and Japan from the combination of the blasts and fires.

It would be years before the US government could provide an accounting of the toll. The Pentagon would make almost no effort to tally the enormous numbers of civilians killed in North Korea by the massive conventional air campaign. But in the end, officials concluded, nearly two million Americans, South Koreans and Japanese had died in the completely avoidable nuclear war of 2019.

Jeffrey Lewis is a scholar at the Middlebury Institute of International Studies at Monterey, California