Editor’s note (9/9/2016): North Korea claimed to have conducted its fifth underground nuclear test on Friday. The explosion created a magnitude 5.3 earthquake, according to officials in South Korea, indicating that North’s nuclear devices are becoming increasingly powerful. The country’s first test, in October 2006, produced a magnitude 4.3 tremor and had a yield of less than one kiloton of TNT. The latest test seems to have produced a force equivalent to about 10 kilotons of TNT.

North Korea has been threatening its neighbor to the south as well as its U.S. ally with invasion and destruction for more than 60 years. Backed by China, the North made good on the first part of this promise in June 1950, sparking the Korean War. But for the most part the decades of hostile rhetoric since the 1953 armistice that ended the fighting have amounted to little more than minor skirmishes. It’s easy to dismiss North Korea’s latest round of pronunciations and posturing as more of the same, except for one important variation in the Kim Jung-un regime’s verbiage. This time around the threat is “thermonuclear” war, and it comes about two months after North Korea’s third nuclear test prompted the U.N. Security Council to pursue additional sanctions against the North.

Taken on its own, North Korea’s recent saber rattling is not much different from what the country has done in the past. The Kim regime earlier this week warned foreign embassies in its capital Pyongyang to consider evacuating by April 10 for their own safety. North Korea this week also withdrew all of its workers and suspended operations in the country’s Kaesong Industrial Zone, which it jointly administers with South Korea, something former leader Kim Jong-il (the late father of the current leader) did three times in 2009. Pyongyang likewise relocated intermediate-range ballistic missiles on mobile launchers—including a couple of untested BM-25 Musudan weapons theoretically capable of reaching Guam 3,500 kilometers away—to its Japan-facing east coast.

Kim Jong-un’s strange proclamations and behavior—including meeting with former basketball star Dennis Rodman—make it tempting to dismiss his regime as ineffectual and out of touch with reality. Yet U.S. officials have taken North Korea’s agitation seriously, even canceling an intercontinental ballistic missile test with the South as part of this year’s joint field training exercises to avoid any misunderstanding that might worsen the situation.

Much of this caution stems from North Korea’s secretive nature and its ongoing efforts to build up nuclear capabilities. The country’s February 12 underground nuclear detonation—about 380 kilometers northeast of Pyongyang—touched off a seismic event measuring between magnitudes 4.9 and 5.2, which correspond to a weapon with an estimated explosive yield of six or seven kilotons. The explosion surpasses the yield of North Korea’s 2009 nuclear test (estimated to have been between two and six kilotons) and a one-kiloton test in 2006.

North Korea has claimed that the February test was to develop a “smaller and light” warhead, according to a report last week from the Congressional Research Service (CRS). (pdf) If so, the test would contribute to North Korea’s ability to develop a warhead that could be mounted on a medium- or long-range missile, although it’s still unclear whether the North Koreans tested a uranium- or plutonium-based device, the CRS report notes.

This matters, according to the CRS, because North Korea is widely believed to have mastered the engineering requirements of plutonium and may now be focusing its efforts on mastering uranium enrichment. The North has also built a uranium enrichment facility at Yongbyon that could produce highly enriched uranium for weapons or low-enriched uranium reactor fuel that could be irradiated for plutonium production. The CRS estimates that North Korea has enough separated plutonium to build several nuclear weapons. In terms of delivering those weapons, the North successfully launched a satellite into orbit in December using a ballistic missile. Still, launching a missile and hitting a terrestrial target are two very different things.

Scientific American spoke with Bruce Cumings, chair of the history department at the University of Chicago, about the events unfolding on the Korean Peninsula. Cumings, the author of several books on North Korea, explains the animosity between the Koreas, the risk of taking the North’s threats lightly and why that country should be allowed to keep any nuclear weapons it currently possesses.

[An edited transcript of the interview follows.]

In the 60 years since the armistice that ended Korean War fighting, the Koreas  have frequently engaged in hostile rhetoric. What is different this time around?
It’s not unusual for North Korea to ramp up pressure and tension on its neighbor to the south when that country and the U.S. hold military exercises, which they do on a regular basis. However, as far as I know this is the first time the North has said it is targeting nuclear weapons at South Korea or the U.S. I don’t know that we’re close to war with North Korea right now, but the threats coming out of Pyongyang lately are an extreme form of what they’ve done in the past. As a result, there’s a hyped-up situation that the White House and the Pentagon have recently been trying to diffuse by putting out word just about every day that there are no unusual troop movements in North Korea, no missiles being readied for launch—except for one or two that the country put on their east coast, probably for a test.

What has kept North Korea from making good on its threats over the years?
North Korea has the capability to inflict huge damage on the South and on Japan. But it has been deterred from launching a serious military offensive six ways to breakfast since 1953, and were they to have launched such an attack at any point in the past 60 years, they would have lost everything they have built since the war ended. They have no effective defense against U.S. airpower and missiles, except to run underground, as they did during the Korean War. They are a unique subterranean people, with some 15,000 underground facilities of a national security nature. In fact, nearly all of their military forces are underground.

North Korea’s latest threats involve the use of nuclear weapons against South Korea and the U.S., yet much of North Korea’s nuclear capabilities are a mystery. What do we know about their ability to launch a nuclear strike?
In general, North Korea has the capability to invade South Korea and cause a horrendous mess, with 10,000 artillery guns in the mountains just north of Seoul and 300,000 to 400,000 crack troops in special forces and guerrilla units. South Korea and the U.S. could defeat a conventional North Korean attack, though it would take half a million U.S. troops, 650,000 South Korean troops and six months to do it. Probably twice the number of troops would be needed to conquer and successfully govern the North. Though I think you would still have warfare going on there for years, a North Korean attack on the South would ultimately mean the end of the Kim regime.

Even if North Korea actually wanted to up the ante by using nuclear weapons, they cannot, to my knowledge, deliver a nuclear weapon on the South short of trucking it across the border, or so-called in situ placement. If they put an A-bomb on a bomber it would be shot down immediately; their missiles do not have nuclear warheads to the best of my knowledge.

What keeps South Korea and the U.S. from preemptively ending any nuclear threat from North Korea?
Paradoxically the U.S. and South Korea are in a similar position as they were in 1953. They are capable of defeating a North Korean invasion of the South, but invading, occupying and governing the North would still be a monumental task. The North Koreans have another 700,000 or 800,000 in their army—in addition to their special forces—that probably aren’t crack troops, but that’s an awful lot of people to deal with in a very mountainous country with all sorts of underground facilities. I think it would be a nightmare to defeat North Korea and try to unify the peninsula. And what would China do if U.S. troops again arrived at their Yalu [River] border? There is no military solution in Korea.

In response to North Korea’s most recent nuclear test in February, the U.S. and its allies tightened sanctions against the North. Is this a potential path to resolving the current hostilities?
These sanctions are a ratcheting up of previous sanctions [prohibiting North Korea from conducting future nuclear tests, giving countries the right to destroy North Korean cargo suspected of including banned materials, denying bulk cash transfers into the country, and freezing any assets or bank accounts tied to the country’s nuclear program]. A new element is that China for the first time worked up new sanctions with the U.S. In the past China has voted for sanctions but didn't actually develop them—and it didn't enforce them. China’s doing this because North Korea decided to make life very hard for China. There is the risk that South Korea and Japan might go nuclear, and North Korea’s words and actions have prompted the U.S. to redouble their missile defenses in the region—which can probably also take out China's intercontinental ballistic missiles.

Sanctions have not worked very well in the past. People, including Sen. John McCain, say that China should cut off its food aid, but that would just be passed down to the little kids and elderly people who will just starve to death. The one sanction the U.S. thinks really worked, and I’m sort of skeptical about it, is [Banco Delta Asia] in Macao that allegedly had $25 million of Kim Jong-il’s personal money. I don’t think things work that way. I think it might have been one of his sons living there. Anyway, North Korea seemed to squawk more at that sanction more than other sanctions, so the U.S. thought that the sanctions were actually biting. But that’s chump change in North Korea, which has a $40-billion gross national product. It’s frustrating to the U.S. because they haven’t found a sanction that’s caused the North Koreans to buckle. They haven’t found any with these new sanctions, and I don’t think they will. Sanctions generally don’t work, and that’s something that [Secretary of Defense] Chuck Hagel used to say as a senator. I hope as defense secretary he does something about that.

How significant is North Korea’s move to suspend work at the Kaesong industrial complex, which it shares with South Korea?
North Korea suspended Kaesong for a few days at a time three different times in 2009. I expect the current suspension will go longer, probably through the big soiree for Kim Il-sung's birthday on April 15th, but I can't believe they will keep it closed for much longer than that because it is such a cash cow for them.

Any serious problems anticipated for the April 15 birthday of late founding leader Kim Il-sung?
They’re too busy contemplating their own navel to do that during these celebrations. I don’t expect the tension to ease until after the U.S.–South Korea war games end at the end of April. But I think the North Koreans have probably gotten much more than they’ve expected out of their antics. They’ve been at the top of the news for the past two weeks, which was probably their goal in the first place. The other thing is they’re building up to the 60th anniversary of the armistice. They are anxious to call attention to their cause and what’s happening on the Korean Peninsula, but they go about it in all the wrong ways.

What is the danger of taking their threats lightly?
We don’t know nearly enough about North Korea’s nuclear program because we have next to no human intelligence in North Korea by which to judge their intentions. We monitor them in every possible way: satellites, infrared photography, U-2 planes are still used—the planes travel along south of the [Korean Demilitarized Zone] with side-looking cameras. At that level, the [National Security Agency] probably can know when a tank starts up at a military base on a cold morning. But there have never been any serious, high-level defections from North Korea, even during the war. The Kim family and their close allies are very good at holding onto power by any means necessary.

It’s very hard for people who don’t know the language and haven’t been to North Korea to understand the nature of the regime, let alone their intentions or their disposition to nuclear war. They’re armed to the teeth. There have been plans for preemption and counter-preemption going back probably to before the Korean War. That’s the logic we’ve been embedded in for 70 years—we contain the North and we restrain the South, and we don’t feel they can be alone with each other without starting another war. One thing that’s been hard for me to understand is the horrible visceral hatred between these two regimes, but ultimately it goes back to a conflict between those who collaborated with the Japanese occupation—1910 to 1945—in the South and those who resisted the Japanese in the North. It was a very brutal colonialism, and if you worked with the Japanese, the North Koreans will hate you and hate your children.

Where does the solution lie? Does the world simply wait for tensions to ease?
I don’t know how I can separate my thoughts from my hopes. I think that there’s still a good chance to engage North Korea and moderate its behavior and normalize its relationship with the U.S. if we’re willing to cap their nuclear program rather than to demand that they give up every last weapon. We can ask for no more production of nuclear weapons and fissile material, but whatever you have you can keep. Because we can’t find them anyway, we never could be sure if they haven’t secreted away a couple of atomic weapons somewhere in their underground. We would also need to give them a very solid security guarantee, which Bill Clinton did in October 2000 when he signed a statement saying our two countries will not have hostile intent toward one another. Pres. George W. Bush just ripped that up as soon as he came into office, as though it never was concluded, and then included them in the Axis of Evil.

Of particular interest to Scientific American’s audience, the U.S. has used nuclear threats and nuclear blackmail against North Korea going back more than 60 years and had hundreds of nuclear weapons in South Korea from 1958 to 1991. The U.S. sends nuclear-capable submarines and aircraft carriers and B-2 bombers up to the shores and has done so just in recent months and days. There is something, to me, that’s vaguely nauseating about a great power like the United States brandishing these horrible weapons in front of what, after all, is a small country of 24 million people, and having done it for more than 60 years. But it never seems to sink in in CNN commentary or most other media commentary that North Korea is certainly a sinner, but it is also a country that’s been sinned against, essentially with threats to eradicate it. [Former Defense Secretary] Don Rumsfeld, in particular, was trying to get Congress to approve nuclear bunker busters for use against Iraq, but especially North Korea because it had built so much underground. But North Korea is its own worst enemy. If I were them, I’d point all of this out in straightforward prose—but they never do that, of course. They’re just as bombastic as they can possibly be.

North Korea from its own standpoint has been betrayed by the United States several times, particularly in the transition from Clinton to Bush. Of course, we think they've cheated on us many times as well. The fact that Saddam Hussein and Muammar Gaddafi gave up their nukes and were then toppled is a key experience for the North—I don’t know what kind of security guarantee you give to North Korea in the aftermath of that. But I know they want good relations with the U.S. and at some point we’re going to have to accept that they are not going to give up all their atomic bombs. That’s a route to quieting things down and maybe normalization, but I can’t see Obama doing this for another year, if he ever does it. It’s just a very bad atmosphere that mainly the North Koreans have created.