2016 has so far been an interesting year for those of us with an eye on the world of nuclear politics and proliferation. To ring in the New Year, North Korea conducted its fourth ^[1] nuclear test on 6 January—the claimed ^[2] detonation of a hydrogen bomb. In the months since, it’s disguised a long range missile test ^[3] as a satellite launch, tested medium range ^[4] and intermediate range ^[5] ballistic missiles, fired ^[6] a submarine-launched ballistic missile and claimed to have miniaturised ^[7] nuclear warheads. All those developments suggest a North Korean nuclear program that’s gaining traction and speed (as I’ve argued ^[8] previously).

There are a number of issues ^[9] with Pyongyang’s flurry of activity in this area. First, each test—whether a success or failure—is a useful learning experience for DPRK scientists and engineers. Second, the further North Korea develops in nuclear capability, the more difficult it becomes to reverse. And third, a more nuclear capable DPRK puts pressure on Japan and South Korea to adapt their deterrence strategies accordingly.

Add to the mix recent comments ^[10] by Donald Trump—currently the presumed Republican nominee for the US presidential election—about the costs and risks associated with America’s military commitments to Northeast Asia. His suggestion that Tokyo and Seoul might need to start protecting themselves, via proliferation if necessary, contradict ^[11] half a century of US foreign policy. Trump’s remarks saw some pundits justifying ^[12] the value of those commitments and others considering the merits ^[13] of his argument.

These developments call into question something often taken as ‘fact’: US extended nuclear deterrence to Northeast Asia. The extension of America’s nuclear umbrella has previously deterred South Korea from pursuing its own nuclear capability and underpins Japan’s non-nuclear stance. But the actions of North Korea and developments in the US have threatened to undermine the credibility of this deterrent. In Japan, we’ve witnessed the head of the Cabinet Legislation Bureau state ^[14] that the Japanese constitution doesn’t necessarily ban the use of all kinds of nuclear weapons. Whilst there are a number of normative ^[15] and cultural ^[16] barriers to pursuing an actual nuclear capability in Japan, a US that walked away from the doctrine of extended nuclear deterrence would open the floodgates to a serious reconsideration of Japan’s nuclear identity.

South Korea’s an even more pressing case. Seoul has pursued ^[17] a nuclear weapons program in the past—in the mid-1970s under President Park Chung-hee—but was eventually deterred by US pressure and assurances. After the DPRK’s fourth nuclear test, however, conservatives in South Korea have been increasingly vocal ^[18] about reconsidering the nuclear option. The former leader of the governing Saenuri Party, Chung Mong-joon, said that South Korea should consider breaking away ^[19] from the Non-Proliferation Treaty ^[20] (NPT) and highlighted the contradictions in its system which failed to prevent North Korea from acquiring nuclear weapons.

The NPT is the most widely adhered to multilateral disarmament agreement. It entered into force for a period of 25 years in 1970, was extended indefinitely in May 1995 and has a total of 190 parties. North Korea is the only country to have joined the NPT, withdrawn under Article X ^[21]—which allows parties the right to withdraw if its national interests are threatened—and gone onto develop a nuclear capability. India, Pakistan and Israel currently sit outside the NPT and all have acquired nuclear weapons.

If the credibility of US extended deterrence is seriously undermined in Seoul or Tokyo, or let alone removed altogether, we would need to think much more seriously about the possibility of another state ‘going nuclear’. If that happened, the number of states with nuclear weapons outside the NPT will equal the number in it (five and five). And regardless of who the next proliferator might be, any new nuclear state could push others to follow. In Northeast Asia, a nuclear weapons program in South Korea might lead Japan and Taiwan to consider their options. What happens to the NPT when there are more nuclear weapon states outside than inside?

If we’re going to start thinking seriously about the future of nuclear proliferation, we also need to start thinking about the future of the NPT. It’s debatable whether the NPT (and the non-proliferation regime that supports it) can survive another country crossing the threshold; but it’s hard to assume that such an event wouldn’t seriously undermine its already cracked foundations. Still, cracked foundations might be better than none. Despite its problems ^[22], the regime codifies both a principle and an objective—nuclear minimalism and eventual disarmament—that the vast bulk of its signatories take seriously. Moreover, the NPT and its associated structures are important to ensuring the peaceful uses of nuclear energy, the control of dual-use technologies and the safety and security of nuclear materials. Even in a more densely proliferated world, that’s a set of principles, objectives and controls we shouldn’t lightly throw aside.

Given the developments of the first few months of 2016, the grim truth is that we can no longer take the future of the global nuclear non-proliferation regime for granted. We can, however, explore where it can be strengthened—and, maybe, what might come after.