North Korea, a small and poor country facing far stronger adversaries and the perpetual threat of its own collapse, would not seem a likely state to defy four consecutive American presidents.
Yet it is precisely that weakness, analysts say, along with the country's history and internal dynamics, that drives its leaders to pursue nuclear and missile programs at virtually any cost — and that robs the world of almost any option to limit them.
Those factors, when viewed together, show why Barack Obama warned President Donald Trump that North Korea would be the gravest foreign threat he faced — and why a solution has proved so hard to find.
Vice President Mike Pence, speaking in South Korea on Monday, cited Trump's "strength" and willingness to use force, warning, "North Korea would do well not to test his resolve."
But Trump may find that North Korea is driven by dynamics more complex than can be solved with strength or threats alone.
WHEN PEACE IS RISKIER THAN THREAT OF WAR
North Korea's nuclear and missile programs are central to a strategy meant to stave off a threat greater than any foreign adversary: the undermining of the North Korean system.
For much of the Cold War, North and South Korea were at roughly comparable levels of economic and political development. Both could claim, at least internally, to be the rightful government of the Korean people who had been temporarily disunited.
But by the 1990s, the South enjoyed a booming economy and a blossoming democracy. Communist governments worldwide were collapsing, and North Korea seemed likely to follow.
Kim Jong Il, then the leader, responded with the "Songun," or military-first, policy, which marshaled the nation to prepare for a war said to be just around the corner.
This policy sought to explain the country's shortages and rationing as necessary to maintain its immense military, to justify oppression as necessary to root out internal enemies and to rally the nationalism that often comes during wartime.
B.R. Myers, a North Korea scholar at Dongseo University in South Korea, wrote in a 2010 book on North Korean ideology, "It is the regime's awareness of a pending legitimacy crisis, not a fear of attack from without, which makes it behave ever more provocatively on the world stage."
Today, the country and government appear to be stable. But this came at a cost: a permanent state of near-war to stave off the forces of history that would otherwise tear down North Korea. Neither threats nor concessions from outside have proved able to override this calculus.
A PERPETUAL STATE OF ALMOST-WAR
The Korean War, never officially resolved, was long deadlocked between the Cold War superpowers. When Soviet protection fell away, North Korea became suddenly vulnerable against the vastly more powerful United States and its allies.
Kim, unable to seek peace without risking a German-style reunification that would subsume the North under South Korean rule, sought to make any potential war too costly to consider.
Missile and nuclear tests, along with what appears to have been a cultivated appearance of irrationality, put the onus on North Korea's enemies to manage tensions.
At first, analysts believe, weapons programs were intended to one day be traded away in a grand bargain with the United States.
But each round of provocation, in deliberately raising the risk of war, made the missile and nuclear programs not just symbolically useful but also strategically necessary.
After imposing such threats on its neighbors, North Korea could hardly drop these programs without understandably fearing an attack. Disarmament, in this view, would invite annihilation.
A DESIRE FOR EXTREME RISK
North Korea's calculus, analysts believe, drives it toward a specific goal: a program powerful enough to survive all-out war with the United States.
Far more powerful states, like Russia or China, dedicate billions in spending and decades of research to similar goals. Small, impoverished North Korea, unable to match their abilities, has compensated with a willingness to accept extreme levels of risk.
Its plan, analysts believe, is to halt any U.S. invasion by launching nuclear strikes at the ports and airfields in the South where troops would enter the peninsula. It would then threaten to launch nuclear-armed intercontinental missiles (an ability it does not yet possess but is developing) at major U.S. cities, forcing the United States to stand down.
By edging up to the line of such a war, North Korea can also coerce its adversaries in peacetime.
Denny Roy, a political scientist who studies Asian security issues, told me last fall that North Korea "intentionally employs a posture of seemingly hyper-risk acceptance and willingness to go to war as a means of trying to intimidate its adversaries."
This puts the world in a quandary: How could any outside threat possibly exceed the risk that North Korea already takes on itself? How could any concession remove the North Korean weakness that drives its behavior?
A HAIR TRIGGER TO NUCLEAR ESCALATION
The United States' relative strength is also, paradoxically, a weakness. North Korea knows that it would quickly succumb to a full U.S. attack, making its only option to escalate to nuclear strikes almost immediately at the start of a conflict.
North Korea also fears that the United States might seek to depose its government in rapid strikes against the leadership, a threat it seeks to deter with repeated warnings of a nuclear response.
In this way, North Korean weakness constrains any U.S. options. Punitive strikes, which might otherwise be used to chasten the country, or strikes meant to degrade the missile or nuclear programs, would risk stirring North Korea's fear of an all-out attack, leading to nuclear conflict.
The Nixon administration faced this problem in 1969, when North Korea shot down a U.S. Navy plane, killing 31. Though the president was willing to bomb Cambodia and Laos and proposed using nuclear weapons in Vietnam, he concluded that even a symbolic retaliation against North Korea would be too risky.
A UNIQUE TOLERANCE FOR PAIN
Iran was persuaded to surrender most of its nuclear program by sanctions, which put the government under domestic pressure from citizens who hated their isolation and poverty and from elites who foresaw huge gains from sanctions relief.
But North Korea has proved itself capable of withstanding economic devastation far exceeding Iran's.
In the 1990s, North Korea was plunged into a famine that killed up to 10 percent of the population. But it neither succumbed to internal unrest nor sought to end the crisis by opening up to the outside world.
The famine, Myers wrote, "may have strengthened support for the regime by renewing the sense of ethnic victimhood from which the official worldview derived its passion."
"Many migrants remember a widespread yearning for war with America during the famine," he added.
This is why some analysts doubt that even the most extreme sanctions, including perhaps those imposed by China, could change North Korea's calculus. Since the famine, though North Korea's economy has grown reliant on Chinese imports, the country has overhauled its food system. It has responded to past Chinese sanctions with provocations, as if daring Beijing to test the regime.
AN ABILITY BEYOND REMOVAL
Some rogue weapons states, such as Iraq under Saddam Hussein, rely on imported technology or assistance. North Korea's programs, however, appear largely indigenous.
This means that, while specific sites could be shut down or weapons removed by a potential agreement or set of strikes, the knowledge to reconstitute them may be there for good.
If North Korea remains bent on acquiring a nuclear-capable intercontinental ballistic missile, then no obvious action short of all-out war could completely derail this drive. Cyberattacks, for instance, can only slow its progress.
North Korea is believed to have short- and medium-range missiles and rockets hidden around the country. Strikes to rapidly destroy these weapons, analysts believe, would be unlikely to succeed before the country could launch at least some.
Seoul, the South Korean capital and a city of 25 million, would be a likely target. Any strike plan, whether to disarm North Korea or punish it, would have to ask whether this was an acceptable risk.
THE HIGH COSTS OF A DEAL
Any agreement that North Korea would be likely to consider minimally acceptable would come at huge cost to the United States and its allies. North Korea would be likely to require:
• A tacit acknowledgment of the country's right to retain its existing programs.
• A declaration that the United States considered the North Korean government legitimate and would not seek to topple it.
• The lifting of sanctions.
• The withdrawal or reduction of the U.S. military commitment to South Korea.
"They want to see the end of that alliance," said Joshua H. Pollack, editor of the Nonproliferation Review, suggesting that North Korea has drawn inspiration from the way that the United States broke with Taiwan in order to normalize relations with China in the 1970s.
Pollack emphasized that North Korea probably saw this as a long-term goal to be accomplished over many years, rather than something to demand up front and all at once.
Still, he said, North Korea may see this as the only way to reduce the existential threat that its weapons program is meant to curb.
Any partial or full American withdrawal would risk sending the American relationship with South Korea and Japan into crisis, empowering North Korea and weakening U.S. influence in Asia.
Even if a president deemed these costs worthwhile, he or she might find the politics of such a deal insurmountable.
A DRIFT TOWARD DISASTER
As time goes on, analysts say, the risks only grow.
"If the current action-reaction cycle continues," Daryl G. Kimball, executive director of the Arms Control Association, wrote in a recent policy brief, "it will not only diminish the prospect of denuclearization of the Korean Peninsula, but it will increase the risk of a devastating nuclear war."
John R. Bolton, the Bush administration's ambassador to the United Nations, told Fox News this week that the only "way to end North Korea's nuclear weapons program is to end North Korea" by bringing about the government's total collapse.
Pollack, asked if he agreed, at first dismissed Bolton as a "hard-liner," saying a war would risk nuclear devastation, but then he acknowledged that the assessment of North Korea's determination was probably correct.
"They're not going to give this stuff up," Pollack said.