Very late on Tuesday, North Korea claimed that it had tested a hydrogen bomb, an especially powerful type of nuclear weapon. Experts are skeptical that the North Koreans actually detonated a full hydrogen bomb, but the evidence does suggest that some kind of smaller nuclear weapon went off.
To understand why North Korea would do this, why it even has a nuclear program, and what this program means for it and the world, you need to understand the history of North Korea's program: where it came from and how it's changed over the years. So here's a brief guide to that program, written to help you put Tuesday's test in context.
1991: The collapse of the Soviet Union
From the division of the Korean Peninsula and the creation of North Korea in 1945 up until 1991, Moscow was its ally and sponsor. The Soviets provided North Korea with huge amounts of economic aid and security assistance, propping up the country. As a superpower patron, the Soviet also provided North Korea with diplomatic and military support.
So when the Soviet Union began collapsing in 1989, and ultimately dissolved in 1991, North Korea was left a precarious position. China filled in the void somewhat, but the North knew that China had no real affection for it and so wouldn't provide the same level of protection as the Soviet Union did.
"With the collapse of the Soviet Union, North Korea lost its main protector. Its turn to developing nuclear weapons made a lot of sense," Keir Lieber, a professor at Georgetown who has studied the thinking behind North Korea's nuclear program, told me. "What does it have that can counter conventional US power? The answer is obvious: nuclear weapons."
1994: The Clinton administration makes a deal with North Korea
The international crisis over North Korea's nuclear program has been around almost as long as North Korea's modern nuclear program. In March 1993, the country announced it would withdraw from the Non-Proliferation Treaty (NPT), which bars non-nuclear states from starting nuclear weapons programs. A month later, the International Atomic Energy Agency (IAEA) said it could no longer verify that North Korea was using its nuclear material for peaceful purposes.
The Clinton administration sat down with North Korea to try to negotiate a deal that would prevent it from acquiring nuclear weapons. In 1994, the US and North Korea announced a deal called the Agreed Framework. North Korea agreed to dismantle its nuclear reactors and accept wide-ranging inspections in exchange for diplomatic and economic concessions from the United States.
From North Korea's point of view, this was a way to take advantage of its nuclear program without actually building nukes. "Pyongyang chose to capitalize on the political and diplomatic utility of nuclear weapons by accepting crippling limits on its plutonium-based fissile material program in return for a better relationship with the United States that would diminish external security threats," Wit and Ahn explain.
But the deal was far from an inevitable success. In order for it to work, North Korea had to continue believing that adhering to the deal was a better way to protect North Korea's security interests than flouting it would be. And this didn't last forever.
1994–1998: North Korea's famine and the Songun policy
In 1994, North Korea's longtime dictator Kim Il Sung died and was succeeded by his son, Kim Jong Il. At the same time, North Korea suffered a famine so severe that much of the population died. (Reliable estimates of the famine's death toll are hard to come by, but estimates range between 600,000 and 2.5 million during the '90s.). The collapse in Soviet aid and trade after 1991, together with a series of droughts and floods in the early '90s, collapsed North Korea's food provision system. What happened next is very important to understanding North Korea, and the nuclear program in particular.
Faced with a question of how to secure the North Korean state in the wake of the Soviet collapse, new leader Kim Jong Il developed something called the Songun, or military-first, doctrine. Songun differed from previous North Korean ideology in that it put the military at the heart of the North Korean state.
Under Songun, "the military is not just an institution designed to perform the function of defending the country from external hostility," South Korean scholar Han S. Park writes. "Instead, it provides all of the other institutions of the government with legitimacy."
On this theory, North Koreans' dire poverty is a necessary condition of the state's strength, not a problem. The military needs everything society has to offer in order to protect North Korea from outsiders; civilians' sacrifices are necessary to preserve the state that protects them.
The practical effect of Songun was that the military got all resources first — including rations during the famine while the rest of North Korea starved.
What does this have to do with the nuclear program? It illustrates just how central militarism became to North Korean strategic doctrine — and because the state thus needed an external threat to justify Songun and the civilian sacrifices it called for. The Kim regime clearly concluded that even in the face of utter economic calamity, fully funding the military was the key to the regime's continued survival. Convincing the people that the military was their savior, not economic or social reform, would allow the North Korean regime to stay in place.
That explains why the North, in the coming years, became so attached to the idea of a nuclear weapon. If the nation's legitimacy depended on the vitality of its military, then acquiring the world's most powerful military weapon became important for more than just foreign policy reasons. It was also a way to show the North Korean people that their military was a powerful protector they could count on for their security.
1998: North Korea tests a long-range missile
In November 2015, North Korea fired a test missile of a new type, called the Taepodong-1 — over Japan. This new missile's maximum range was roughly twice that of the North's next-biggest weapon, the Rodong.
This kind of medium-range missile could potentially hold a nuclear payload, if North Korea figured out how to both build and then miniaturize a nuclear bomb. As such, the international community saw this as a profound provocation: Testing a nuclear-capable weapon at a time when negotiations over North Korea's nuclear and ballistic missile programs were still ongoing suggested a clear lack of intent to adhere to the deal's spirit and perhaps letter.
The Taepodong-1 test reveals two important things about the North Korean program. First, North Korea is quite willing to provoke the West when it wants to, even if it jeopardizes international negotiations. This could be either because North Korea is trying to extract concessions or simply because it wants to strengthen its military; scholars disagree. But the point is that it's not obvious how committed North Korea ever was to good-faith negotiations.
"Even in 1994, there's still a question as to whether North Korea was ever committed to abiding by the Agreed Framework," Lieber told me.
Second, North Korea lies about its technological capabilities — a lot. North Korean state media claimed the Taepodong launch put a satellite into orbit; independent data suggested no such satellite reached orbit. It looked like North Korea had tried to send up a satellite, but the object had most likely been blown up when its own fuel tank exploded.
This may seem ridiculous, given that it's easy to verify whether North Korea is lying about stuff like this. But it actually makes a certain amount of sense: North Korea maintains a really tight grip on the media domestically. Exaggerating its military strength helps make the military stronger, thus solidifying the regime's legitimacy in Songun terms.
2001: Bush takes office, US policy shifts
When George W. Bush became president, America's North Korea policy shifted dramatically. While the Clinton administration took an essentially carrot-and-stick approach to North Korea's nuclear program — if you give them some stuff, and threaten other stuff, maybe you can shape their behavior — the Bush team disdained negotiations.
"At its outset, the Bush Administration was generally disinclined to test the incentives-for-denuclearization hypothesis that the Clinton team had explored," Evans J.R. Revere, a Korea expert at Brookings, writes. "Many in the new administration were convinced that North Korea had no intention of giving up its nuclear program at any price. Many were also opposed in principle to providing incentives or 'rewards' to North Korea, a regime they detested, even if this might yield some progress."
As a result, the Agreed Framework — always on tenuous footing given the nature of the North Korean regime — collapsed. "Before the end of 2002, North Korea removed the seals on the 5-megawatt reactor and other facilities at Yongbyon, evicted IAEA monitors, and began the process of restarting its nuclear weapons program," Revere explains.
According to Revere, some Bush officials internally advocated for renewing negotiations, and by 2003 they succeeded. The US and four other interested powers (South Korea, Japan, China, and Russia) — sat down with North Korea to discuss a nuclear agreement. They made some progress: In 2005, North Korea agreed in principle to give up its nuclear weapons program.
But the new agreement, unlike the Agreed Framework, didn't involve temporarily freezing North Korea's nuclear weapons while a final agreement was hashed out. As negotiations dragged on, North Korean research on a bomb continued.
You can read this one of two ways. You could say the Bush administration screwed up a good thing the Clinton team had put in place. Or you could say it showed that North Korea had entered negotiations in bad faith and was always going to pursue a bomb regardless.
Revere thinks it's the latter: "In retrospect, the US inability to attain [an end to the program] owes much more to North Korea’s dogged determination to possess nuclear weapons than to any other factor," he concludes.
It probably didn't help, though, that the Bush administration had launched an invasion of Iraq to topple Saddam Hussein for his supposed weapons of mass destruction — and that Bush had named North Korea alongside Iraq as part of the "axis of evil," perhaps contributing to North Korea's desire for a nuclear deterrent.
2006: North Korea tests its first nuclear weapon
This was the year everything went to hell. In July, North Korea tested the Taepodong-2, its first missile that could theoretically reach parts of the United States — if it had worked, anyway. The test failed, but it raised serious concern about North Korea's intentions.
Then on October 9, North Korea tested its first nuclear device near the village of Punggye-ri.
The device was primitive. It boasted a single kiloton of explosive power at most; the bomb dropped on Hiroshima, detonated more than 60 years prior, yielded somewhere between 13 and 18 kilotons.
But it nonetheless changed the game. Any negotiations would have to start from the fact that North Korea already possessed nuclear weapons rather than attempting to prevent that from happening.
After the test, North Korea signaled that it would be open to denuclearization in official statements. The UN Security Council passed a resolution condemning the test, which also imposed new economic sanctions on North Korea.
The big question then became: How much did North Korea value its hard-won nuclear capability? And would it be willing to give it up in exchange for a relaxation?
2009: North Korea's second nuclear test
This question was answered rather decisively in May 2009, when North Korea tested its second nuclear device. This bomb showed modest technological progress, with a yield estimated to be between 2 and 8 kilotons. But the most important element of the test was the signal: North Korea was, clearly, still committed to expanding its nuclear arsenal.
The UN Security Council slapped more sanctions on North Korea, but it was hard to give them much bite. North Korea's economy was already broken, having been walled off from most international trade since the end of the Cold War. Clearly, the Kim regime was willing to suffer international isolation and economic deprivation in the name of preserving its nuclear arsenal.
This, in essence, has been the status quo for North Korea nuclear policy ever since. The North Koreans aren't willing to give up their weapons now that they've built them, and there's just not a whole lot the United States or South Korea can do to punish them for the program. The Obama administration has attempted to revive Clinton-style negotiations but, given the contours of the situation, haven't made it a top priority à la negotiations with Iran.
So the North Korean program keeps on chugging.
"We already don't have diplomatic relations; we've already sanctioned them multiple times," David Kang, a professor at the University of Southern California, told me in an interview last year. "There's not much you can do."
2012: North Korea's missile test fails dramatically
In 2012, North Korea test-launched an Unha-3, a rocket derived from the Taepodong-2 that could serve as a prelude to an even bigger missile. Only the test failed yet again: The missile disintegrated right after launch. The failure was so embarrassing that even the North Korean state media couldn't cover it up; according to the New York Times, "it was the first time the North has publicly acknowledged a long-range missile or satellite failure."
This points to something important: North Korean mastery of nuclear and related missile technology is still thought to be quite rudimentary. While the program poses a very real threat to its neighbors, particularly Japan and South Korea, we don't actually know how may weapons it has or how effective its delivery mechanisms (bombers, submarines). What we do know publicly, though, is that North Korea has a long track record of technological failure.
Take, for instance, the persistent claim that North Korea has nuclear missiles that can hit the United States. This comes from the theoretical range of the Taepodong-2 missile, which at its peak could hit Alaska. But the Taepodong-2 has never demonstrated that kind of reach in an actual test, nor has North Korea demonstrated that it can make a nuclear device small enough to fit on a warhead (though it's conceivable).
North Korea "has had tremendous trouble overcoming various technical hurdles that US experts assumed would not pose any serious difficulties at all," Jacques Hymans, another USC professor, said in a 2013 interview with the Federation of American Scientists. "Even its recent tests can be said to have been 'successful' only relative to the ridiculously low bar that Pyongyang had set with its prior disastrous test failures."
2013: North Korea's third nuclear test
In 2013, North Korea tested its third nuclear device (this time with a 6 or 7 kiloton yield). This test raised yet another question: If North Korea already had nuclear weapons, why would it need to keep testing them?
There are a number of possible answers. Maybe it was a provocation designed to wring concessions from the West. It's also easy to read this through the lens of Songun: North Korea needs to keep demonstrating military advances, even fictional advances, to show the people that the military is strong enough to protect them.
But there's a third, simpler explanation, one advanced by Dartmouth professors Jennifer Lind and Daryl Press, along with Lieber, in Foreign Affairs. Writing after this third test, they argued that the right answer was probably the simplest one: These are, in fact, tests designed to improve the quality of North Korea's nuclear arsenal.
This, the scholars note, has historical precedent. "Between 1945 and 1992, the United States conducted 1,054 nuclear tests and fired an untold number of missiles. If the goal had merely been to show the Soviets that the United States meant business, testing nearly twice a month throughout the entire Cold War would have been overkill," they write.
Instead, they claim, North Korea believes its security depends on nuclear weapons, and thus needs to make sure they work. "North Korea's mission requires small, lightweight warheads, and missiles that work," Lind et al. write. "The only way to know that they work is to test them."
2016: North Korea tests a fourth bomb — and claims it's hydrogen
In December 2015, North Korea claimed something that seemed incredible: It had built a hydrogen bomb, which is a more advanced form of nuclear weapon. Then on January 6, after a seismic anomaly occurred within North Korean territory, the country claimed to have actually tested one.
"The DPRK's access to H-bomb of justice ... is the legitimate right of a sovereign state for self-defense and a very just step no one can slander," an official statement from the state-run Korean Central News Agency blared.
Hydrogen bombs work by harnessing energy created by fusing hydrogen atoms together, unlike atomic bombs, which work by tearing apart atoms through atomic fission. This makes hydrogen bombs much more powerful.
"Nuclear weapons employing fusion can have a yield measured in megatons. (A kiloton is 1,000 tons; a megaton is 1,000 kilotons)," Bruce Bennett, a defense analyst at the RAND Corporation, explains in a piece for CNN published when North Korea first claimed to have developed a fusion bomb.
If North Korea had developed a hydrogen bomb, this would be a big step up technologically. But experts were very, very skeptical: The size of the seismic disturbance created by the bomb was similar to past tests, and thus too small to be made by a bomb that was orders of magnitude more powerful.
However, it is possible North Korea is using a sort of in-between weapon called a "boosted" nuclear device. This involves a very small amount of fusion to boost the explosive capability of a fission bomb. According to Bennett, these weapons generally have a yield around 50 kilotons.
"Maybe boosted. Definitely not a successful staged device," Jeffrey Lewis, the director of the East Asia Nonproliferation Program at the Middlebury Institute of International Studies, tweeted.
Regardless, the test shows that North Korea's nuclear knowhow is still expanding (however slowly). "Whatever the type of design of weapon tested by North Korea or its exact yield, this fourth nuclear test has undoubtedly advanced North Korea's technical understanding of their nuclear designs," the Arms Control Association's Daryl Kimball and Kelsey Davenport write.
And there doesn't seem to be a thing anyone can do about it.