North Korea has tested its fifth nuclear weapon — one more powerful than any device it has tested previously. What does this mean for the world?

To find out, I got in touch with Jeffrey Lewis, director of the East Asia Nonproliferation Program at the Middlebury Institute of International Studies at Monterey. Lewis is an honest-to-goodness expert on North Korea’s nuclear program, so what he has to say carries real weight.

And what he had to say was scary.

According to Lewis, the North Korean test shows the country has the capacity to make a bomb compact enough to put it in a missile. This is dangerous: According to Lewis, it raises the likelihood of a miscalculation, which could potentially lead to an actual war between the United States/South Korea and North Korea.

A war isn’t likely because of this test, mind you. But it is more plausible than it was yesterday, which is really scary when we’re talking about conflict between nuclear-armed states.

Lewis and I spoke about why that’s the case, what can be done to limit the threat, and how we got to this situation. What follows is a transcript of our conversation, edited for length and clarity.

Zack Beauchamp: What do we actually know about North Korea’s nuclear test?

Jeffrey Lewis: What we can tell, seismically, is that it was an explosion. Strictly speaking, we don’t know it was a nuclear explosion — but it was a nuclear weapon–size explosion at the North Korean test site on the hour that they say it was a nuclear explosion.

It’s certainly bigger than any other of their tests. We don’t know exactly how big it is: You’re gonna see a range of sizes. But the important thing is that people’s estimate of this event is higher than their estimates of previous events.

My guess is that these tests are larger than we think, because they bury them under a lot of rock and that messes up the signal. This is at least 10 kilotons, and I think it is probably 20 kilotons. There is no question that this thing succeeded.

ZB: So what does this increased size tell us?

JL: It’s a compact device that fits on a nuclear warhead. I assume they use both plutonium and highly enriched uranium. But that’s a guess based on what the North Koreans have said.

The North Koreans said, "This is the bomb that is going to go on the missile force." The language they used is identical, or really similar, to the language they used when Kim Jong Un posed with a mock-up of a bomb. So my guess is that they are the same object: that the mock-up was a bomb that’s going to go on their missile force.

ZB: And you think they’re telling the truth about this?

JL: Yeah, this is a really big thing. They’ve done five nuclear tests; that is a lot. We’re so used to thinking of them as backward, we’ve kind of forgotten that they’re the country that has conducted the sixth most nuclear tests in history.

If you look at what everyone else was able to do by their fifth test, no one was unable to make a nuclear weapon that would fit on a missile.

We shouldn’t assume that countries will struggle to make a bomb that will fit on missiles. And five tests in, with pretty solid yields, I think there’s no reason to doubt them. We should be careful not to hold them to a radically different standard than we’ve held every other country.

ZB: Making a compact device like this could be a pretty big deal, militarily, because it means North Korea can now launch a nuke using a missile rather than having to drop one from a plane. Does this alter the security situation with South Korea and the United States?

JL: I’ve assumed they could do this for a while. What’s different now is that they’re not saying they have the capability. They’re saying that they are doing it.

And this is consistent with a whole bunch of stuff we’ve seen in the last couple of years. [For example], North Korea created a strategic rocket force. It has a headquarters — Kim Jong Un has visited them. So it has an organizational structure that looks like a real nuclear force.

They have really increased the testing of their missiles, which I think suggests both that their production is more robust and that they’re serious about making operational weapons. And now there are standardized warheads that they’re going to deploy.

So it looks to me like they’re moving from "we have this capability" to "we actually are going to have nuclear bombs that are assigned to missile units, and if you attack us, these people are going to nuke you."

That’s gonna be different, for a couple of reasons.

When we thought North Korea had enough plutonium for one or two bombs, the old joke was: "What do you do if North Korea tested one? Tell them to test the other one!" It wasn’t really like "if we have a war, it’s going to be a nuclear war."

That’s different now. They’ve been very clear that their goal for this nuclear force — and this should scare the pants off of us — is to hit ports and airfields and US forces in region. They’re not going to do what Saddam [Hussein] did, which is sit like an idiot in Baghdad and watch us build up.

"Their goal is going to be to kill him so that he can’t shove his fat little finger on the proverbial button"

They did a Nodong [missile] test a few months ago. And they said, point blank, that this is a test of an airburst of a nuclear weapon against enemy ships in port, to keep enemy forces from coming into the [Korean] Peninsula. Now, who’s going to ship forces into Korea? What country is that?

They’re hoping to deter. But if deterrence fails, they’re going to use nuclear weapons to repel an invasion. That means hitting Seoul, hitting Busan, hitting US forces in Japan — and hoping that the shock of that nuclear attack will cause us to stop.

ZB: Jesus.

JL: Flip this around: If you’re South Korea, this is terrifying!

Because if you’re South Korea, you’re thinking, "Crap, if they get itchy in the event of a crisis, they’re going to plaster our whole country with nuclear weapons."

So if you’re South Korea, what’s your plan? Do you think you can go hunt and kill all the missiles? The answer is no.

They talk about missile defense. But I think what they’re really planning on doing, and you see this in their really sophisticated ballistic missile and their cruise missile programs, is that they’re going to try to kill Kim Jong Un.

Their goal is going to be to kill him so that he can’t shove his fat little finger on the proverbial button.

So both North Korea and South Korea have approaches that, I think, push them to use their forces in a conflict — to go first. That would be the textbook definition of "unstable."

ZB: That’s not great

JL: Yeah. Scary, right?

ZB: I had always thought the Korean Peninsula was relatively stable, inasmuch as such a situation can be stable. Neither side had an interest in escalating conflict, and while it was worrying, the balance of forces made it basically stable — because everyone knew there would be catastrophic losses on both sides. You’re suggesting that miscalculation — getting pulled into a war nobody really wants — is a more serious possibility after this test.

JL: Don’t get me wrong — North Korea trying to nuke ports and South Korea trying to kill Kim Jong Un are both desperate measures. We’re probably going to muddle through.

But I think we should be really clear that both sides are building in incentives to go early. So crises may be a little bit hairier, and a little bit more dangerous, than we would expect.

It probably makes sense that we would start thinking about this stuff — like possibly trying to talk to the South Koreans out of the idea that they can kill Kim Jong Un. Trying to persuade them that their missile capabilities aren’t that great: "Hey, we tried killing Saddam Hussein at the beginning of Operation Iraqi Freedom, and we missed! Kim has nuclear weapons, so you don’t want to miss!"

"Think about how bad the Iran debate was, and now try to imagine cutting a deal in which Kim Jong Un gets to keep his nuclear weapons"

But I think also, it’s probably really important to head off the ICBM [intercontinental ballistic missile] program. The North Korean ICBM program is going to be a real problem, because the idea that they’re going to use nuclear weapons all over South Korea and Japan is way less credible if they can’t hold back an ICBM program that’s going to threaten the United States.

They’re trying to imagine this era where they can use nuclear weapons early regionally, and we’re going to be like, "We’ve got to stop, because otherwise LA is going to be next." So if we can head off the ICBM program, then things are going to be a lot more stable.

We can’t, by the way.

ZB: Yeah — it seems there’s no good mechanism for stopping them. We can’t physically interdict parts, and sanctions clearly haven’t worked.

JL: You’re never going to be able to use sanctions to physically prevent a country from building nuclear weapons. You can slow them down, but whatever: The Soviets did it, the freakin’ Chinese under Mao did it. This is not that fancy of a technology.

People hope that you’re going to be able to use sanctions to put political pressure on a government. But, hey, we’ve tried that with North Korea, and that’s not worked.

So what we’re left with is to negotiate. And that’s hard, because they’re unpleasant — an ugly, ugly, ugly government. Nobody wants to sit down to a state dinner with Kim Jong Un while people in North Korea are starving. But the reality is that there’s not any other way to get them to not build this stuff other than to persuade them not to.

And this is a huge problem: The North Koreans have always been super clear that they’re willing to trade away stuff that they haven’t done yet for promises of a better relationship, but they’re not willing to trade away stuff that they have done.

So 20 years ago, when we were talking with them about a missile deal — that was a great deal. They’d built hardly any of these things, so locking them in place — even though we couldn’t get rid of the last few missiles — would have been amazing.

But we were, like, total dicks about it. We were like, "No, no, it has to be everything." And they said, "Okay, we’ll build some more stuff."

Making a deal with North Korea is going to require accepting that they have a certain amount of nuclear capability that will threaten South Korea and Japan. That will be a political nightmare. Think about how bad the Iran debate was, and now try to imagine cutting a deal in which Kim Jong Un gets to keep his nuclear weapons.

Second, the only way you can make that case is for the Bush and Obama administrations to collectively admit that they have fucked it up. To collectively admit they have been politically cowardly, that they have talked really tough while doing nothing — and that whatever deal we’re going to get now is way worse than what we would have gotten in 2001.

ZB: Is this a little window into what we would have been seeing, in a few years, if there hadn’t been an Iran deal to cut off Iran’s nuclear pathway?

JL: Oh, God, yeah.

This is why I’m so frustrated with the people who are against the Iran deal. If we had bombed them, and they had gone the North Korea route, then in 10 years we’d be exactly where we are with North Korea. President Ivanka Trump would be issuing a statement about how she’s not going to accept a nuclear Iran and North Korea.

That’s ultimately our problem. We don’t have any tool other than negotiating with [rogue states]. And negotiating with them is hard because they’re ugly, and it requires admitting that our strategies for the past 15 years have been a total sinkhole.

How deterrence is changing, explained by Ash Carter