Editor’s Note (8/29/17): Scientific American is re-posting the following article, originally published August 11, 2017, in light of claims by South Korean and Japanese officials that North Korea fired a ballistic missile over Hokkaido, Japan’s second-largest island, early Tuesday morning. The missile flew about 2,700 kilometers before landing in the Pacific Ocean to the east of Japan. This was the third time North Korea has fired a projectile over Japan since 1998.

The disturbing news earlier this week that North Korea has likely miniaturized a nuclear warhead that can fit on a long-range missile has been intensified by the news on Thursday that the country is supposedly drawing up plans to fire four of them toward Guam, a U.S. island territory in the western Pacific Ocean. Military threats by North Korean leader Kim Jong-un’s regime against the U.S. and its allies are nothing new, but recent intelligence reports coupled with last month’s test of an intercontinental ballistic missile (ICBM) possibly powerful enough to reach parts of the U.S. suggest North Korea might soon have the technology to back up those threats.

Analysts have been speculating for more than a year that North Korea—formally known as the Democratic People's Republic of Korea—was quickly working toward the goal of building a nuclear warhead small enough to fit on an ICBM. In March 2016 Kim Jong-un’s regime released a series of propaganda photos of the dictator standing next to a shiny silver ball—jokingly referred to as the “disco ball”—which was later determined to be a model of a mini warhead.

Tensions between the U.S. and North Korea have fluctuated over the past decade since Pyongyang’s first nuclear test in 2006. For the most part North Korea’s nuclear detonations and missile tests have been met with sanctions and joint military exercises between the U.S. and South Korea aimed at deterring Kim Jong-un’s nuclear ambitions.

Escalating rhetoric between President Donald Trump and Kim Jong-un over the past few days has ratcheted tensions as high as they have been in years. Scientific American reached out to Patrick Cronin, senior director of the Washington, D.C., think tank Center for a New American Security’s Asia-Pacific Security Program, to better understand how we reached this point, and what to expect next.

[An edited transcript follows.]

How would the U.S. Defense Intelligence Agency determine the country has miniaturized a nuclear warhead to fit on a missile? 
DIA would use [information from a variety of sources] to make an informed estimate of the threat. Detailed analysis would differentiate between what has been verified and what has been extrapolated. For instance, the famous disco ball photo of Kim Jong-un has been analyzed as representing miniaturization minus the re-entry and guidance technology. The most recent ICBM test launch suggests progress on a re-entry vehicle. So, putting together even open-source information, it seems prudent for an intelligence analyst to estimate that North Korea has achieved these capabilities. Pyongyang has been working on these systems for a long time, and they are a priority for Kim Jong-un. Nobody outside North Korea knows the precise capabilities in Kim's possession, but the estimate appears to be an attempt to provide some outer limits to those capabilities—to make them public before Kim seeks coercive advantage by 'surprising' the outside world with future technological demonstrations or parades.

How are sanctions intended to disrupt North Korea’s plans to build a nuclear arsenal?
Targeted sanctions can help slow down North Korean programs and impose penalties on Kim and North Korean elites, including those associated with entities involved in [weapons of mass destruction] and missile programs. Sanctions are one means of exerting pressure, just as the possibility of removing sanctions is a means of providing an incentive to desist from certain activities. Sanctions are thus part of a larger carrot-and-stick policy to steer North Korea toward a more agreeable negotiating position. Unfortunately, the overlapping interests between North Korea and the United States are limited to broad objectives such as avoiding nuclear war. That is, Pyongyang wants to be a permanent nuclear weapon state and the United States is committed to a denuclearized Korean peninsula, and that leaves little middle ground.

Thus, the administration is focused more than previous governments on secondary sanctions on those entities doing business with North Korea. That is largely focused on China, and here sanctions are meant to inconvenience, cajole and otherwise persuade China to exert greater pressure on North Korea. Washington is leaning on Beijing to lean on Pyongyang to return to the bargaining table and refrain from a sixth nuclear test or deploying an ICBM.

Will that strategy work?
Probably not. So that means for the time being we are stuck in a dangerous if manageable stalemate. If North Korea doesn't find at least tactical relief through diplomacy now, perhaps it will seek such a respite in the coming months. But that doesn't mean during this ongoing, evolving, intensifying standoff and cold war, we [won’t be] able to fashion some useful diplomacy. Confidence-building measures to avert inadvertent escalation or accidental uses of force might be possible. Over time, a thaw or detente could set in as well. But for now, barring more political will from Pyongyang to slow down on deploying nuclear-tipped intermediate-range ballistic missiles [IRBMs] and ICBMs, we should be prepared for greater deterrence and brinkmanship.

How significant are North Korea’s threats against Guam?
As the Obama, and now Trump, [administrations have] used B-52 and B-1B bombers based in Guam to demonstrate resolve and underscore deterrence, Pyongyang has spewed vitriolic and threatening statements toward the United States and especially U.S. military bases in the region. As a result, North Korea has implicitly threatened Guam in the past. Recent advances in the country’s missile range demonstrated especially since last year now give the threats a patina of credibility. The threat of firing missiles to Guam is partly an indication of what Kim thinks he might be able to do.

Does North Korea have missiles that are reliable enough to follow through on its threat?
Although firing four unarmed IRBMs of questionable reliability toward Guam could well produce a lethal accident that demands some response from the U.S., the risk might be worth it to Kim. He may calculate that testing would not trigger a war and could make the United States look weak, at least in the absence of a strong U.S. response. Kim is probing the limits of non-lethal force, emboldened by his newfound capabilities, but he is definitely not looking for a real war. He wants the Western media to do his bidding, to convert his still limited WMD arsenal into a sufficient capability to intimidate audiences at home and abroad. The United States has no intention of initiating a conflict and is well aware of the stakes. But the President wants to be unequivocal about U.S. capability and will to respond to any attack on the United States or our allies.

How important will negotiation be, compared with building our anti-ballistic missile capabilities?
It is easier to see how this cold war is prolonged than ended. More defense is something we know how to do and together with allies can further strengthen, to preserve deterrence and contain the coercive benefits Pyongyang seeks to extract from saber rattling. Sudden war will remain a remote if non-trivial possibility, of course, but the probability is a protracted standoff and cold war relationship punctuated by bouts of diplomacy, possibly risk-reduction measures, perhaps even some type of a detente. In the longer run, the most likely peaceful end for Northeast Asia would be internal change that comes from within North Korea. Ironically, the building of intervention-stopping nuclear weapons hastens the day when Kim has to deliver economic goods to more people or risk losing legitimacy thus far based on the fear caused by nuclear-tipped missiles.