My colleague Andrew Davies has written ^[1] convincingly about the challenges of securing a diplomatic resolution to the North Korean nuclear crisis. He speculated about a solution in which the US accepts North Korea’s nuclear status at the current level of development while maintaining the status quo posture for American and allied forces and diplomacy. The idea is to avoid the worst possible short-term outcome of a major war that could escalate rapidly past the nuclear threshold. However, he recognises that a lack of trust makes such a solution very tenuous, and it may not be possible to achieve.

So, what happens if, in the absence of a diplomatic solution that leads to verifiable North Korean denuclearisation, we’re left with a fait accompli because we’re unwilling to consider preventive war ^[2] as an alternative? Accepting North Korea as a nuclear weapons state doesn’t end the crisis. Pyongyang would continue the rapid modernisation of its nuclear weapons technology and missile capabilities. Furthermore, if the US and its allies weren’t prepared to wage war, Kim Jong-un would have little incentive to submit to limitations on his nuclear forces, or accept verification and monitoring through an intrusive inspections regime that would clip his nuclear wings.

Instead, the next likely step for North Korea beyond a demonstrated nuclear-capable ICBM would be submarine-launched ballistic missiles (SLBMs) based on further development of the Sinpo-class ^[3] experimental ballistic missile submarine (SSBA). Acquiring a nuclear second-strike capability makes sense for North Korea.

One of the steps that the US and South Korea would take in the face of accepting North Korea as a nuclear weapons state would be deploying the means to undertake non-nuclear pre-emptive attacks against North Korean land-based nuclear forces, command and control, and leadership. North Korea’s Sinpo-C SSBA ^[4]could carry a small number of SLBMs based on the Pukguksong KN-11 missile ^[5], and these would be able to threaten South Korean or Japanese cities and preclude such strikes. Over time, that would also make it more difficult to deter North Korean provocations below the nuclear threshold, particularly if North Korea became skilled in operating such submarines in ‘bastions’ in the Yellow Sea or the Sea of Japan.

Its land-based ballistic missiles would become more effective, and more capable of delivering nuclear warheads accurately. The Center for Strategic and International Studies notes ^[6] that North Korea is already working on a manoeuvring re-entry vehicle (MaRV) for its KN-18 short-range ballistic missile. MaRVs ^[7] would give North Korea greater ability to penetrate South Korean, Japanese and US missile defences. This technology could then be retrofitted to other longer-range missile systems, so missile defence as a solution becomes more uncertain over time. Nor is there any reason why North Korea couldn’t develop higher-yield warheads, now an apparent trend following the sixth ^[8] nuclear test on 3 September 2017. Future tests are likely, although North Korea is clearly facing a problem at its Punggye-Ri nuclear test site ^[9] and the risk of collapse of underground tunnels may in part be driving its suggestions of future atmospheric nuclear tests ^[10].

In considering where these developments may lead, we need to remember why North Korea is seeking nuclear weapons. Ensuring regime survival and deterrence of external threats that could lead to regime change is a key justification for North Korea’s nuclear and missile programs. It also wants to win acceptance as a nuclear weapons state and gain entry to the elite club of nations with such weapons. That would dramatically strengthen Kim’s power internally. He might be prepared to talk from behind an enhanced and survivable nuclear shield, with his power base secure, having forced the US to ‘blink first’ in the crisis, but his ultimate goal would be to see the US reduce its presence in and commitment to South Korea.

China and Russia have promoted a ‘freeze for freeze’ deal ^[11], in which North Korea supposedly halts its nuclear and missile development in return for the US ending joint military activities with South Korea. If that proposal were accepted, it would contribute to the goal of decoupling the US from its allies in Asia. But it would be difficult to verify North Korean compliance, especially if, as is likely, North Korea didn’t allow intrusive inspections. It would also be hard to prevent North Korea from using computer simulation to further develop warhead designs.

The risk is that if we accept the status quo now, then an assertive China, along with Russia, may see an opportune moment to double down on freeze for freeze, on the understanding that North Korea might then come to the table, but from a perceived position of strength, and potentially with a much larger and more capable nuclear arsenal likely to emerge in a few years.

In this scenario, there would likely be increasing pressure on South Korea, and Japan, to consider their own nuclear deterrent capabilities. That would have drastic consequences for the success of nuclear non-proliferation across much of Asia. In the face of such pressure, the US would have to choose between boosting its extended nuclear deterrence security guarantees and watching nuclear non-proliferation in Asia collapse.