The overwhelming consensus in the U.S. foreign policy community is that a nuclear-capable North Korea is perfectly acceptable since North Korea can simply be deterred. As Vipin Narang and Ankit Panda put it in their analysis of the Singapore summit’s failure to bring about North Korean denuclearization, "the significant silver lining is that [the Singapore summit] could lead to a stable deterrence relationship between the two countries."
The history of how deterrence actually worked during the Cold War shows that any deterrence arrangement between the U.S. and North Korea will necessarily be subject to a substantial risk of catastrophic failure. The only way to avoid exposing the U.S. to an unacceptable risk of a nuclear strike by a vastly more powerful North Korea in the future is to bring about the complete, verifiable, and irreversible denuclearization (CVID) of North Korea today–by diplomacy if possible (as unlikely as that now appears) or by preventive war if necessary.
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The logic of the deterrence option is essentially this: A) Kim is rational and wishes to preserve his regime; B) Any use of nuclear weapons by North Korea will lead to a retaliatory strike by the U.S. that would end Kim's regime; therefore C) Kim will not use his nuclear weapons against the U.S. or its allies. I admit that this logic does sound superficially persuasive...unless one has thought about financial crises. Here we can rephrase the "deterrence works" syllogism to: A) Bankers are rational (at least as rational as Kim Jong Un); B) A financial crisis is bad for bankers (undoubtedly true); therefore C) Banks will not act in a way that brings about a financial crisis. However, the 2008 financial crisis still happened. What went wrong?
Let me begin by noting that financial deterrence worked (in a fashion): the fact that a financial crisis is bad for bankers meant that the financial crisis wasn't caused by 17 financiers waking up in New York one morning and randomly deciding to wreck the global financial system. The crisis happened regardless because individually rational decisions that made sense to the people who took them at the time interacted in ways that exposed the financial system as a whole to the risk of a catastrophic failure (systemic risk). If systemic risk is high and if you play financial crisis roulette for long enough, you lose.
So, in the absence of CVID, the U.S. will be forced to play deterrence roulette with North Korea. Just how risky would that be?
As the long history of financial crises demonstrates, this question isn't about the risk that Kim acts irrationally (nobody thinks that Kim is going to wake up one morning and randomly decide to nuke Los Angeles). The question comes down to this: how much risk is built into the system when everyone behaves rationally? And here the evidence indicates that any deterrence arrangement between the U.S. and North Korea will inevitably be subject to an enormous amount of systemic risk. In this situation, it would be exceedingly rash to bet that the U.S. will never lose a round of deterrence roulette.
North Korea seeks to obtain nuclear weapons to prevail against the U.S. if the U.S. acts to prevent North Korea from achieving objectives that harm the U.S. and/or its allies (a nuclear crisis episode). As Matthew Kroenig's new analysis of nuclear strategy shows, countries rationally seek to prevail in these situations by acting to increase the probability of a nuclear exchange. As this probability ratchets up, each country weighs the expected consequences to them of a nuclear exchange against the importance of their objectives. Eventually, as the risk of a nuclear exchange increases, one country throws in the towel and the other one wins. Alternatively, a nuclear war happens.
History shows that crisis episodes have come very close to ending in nuclear war. During the Cuban Missile Crisis, for example, the captain of a Soviet sub came under the mistaken impression that he was being attacked by the U.S. and would soon be sunk. He seriously contemplated using a nuclear-armed torpedo to destroy a U.S. aircraft carrier first (he was talked out of doing so by other senior officers on board). Given that the U.S. military was on a hair-trigger alert at the height of the crisis, any Soviet attack that killed thousands of Americans–let alone one with nuclear weapons–would surely have led to war. Reflecting upon the crisis, Graham Allison wrote that "Kennedy thought the chance of escalation to war was 'between 1 in 3 and even', and what we have learned in later decades has done nothing to lengthen those odds".
Even without the protection that nuclear weapons provide, North Korea has attacked U.S. military assets , raided Japan and kidnapped Japanese citizens , sunk a South Korean ship , shelled South Korean territory , bombed a South Korean passenger jet , provided military assistance to hostile powers , and engaged in extensive cyberwar operations against the U.S. and its allies. Given this track record, North Korea will almost certainly act in a way that provokes a crisis in the future .