There were subsequent scares, of course, most notably the 1962 Cuban Missile Crisis. For the most part, however, nuclear weapons largely remained in the background during the Cold War. The US and the Soviet Union (followed by Russia) built robust arsenals that minimized any advantage to striking first. In addition to deterrence predicated on mutual assured destruction, arms-control agreements provided both governments with the transparency and predictability they needed to avoid costly and dangerous arms races.

This has all taken on increased relevance as New START, the final nuclear arms control accord limiting the arsenals of the US and Russia, expired last week. It was Vladimir Putin, of all people, who offered to extend it informally (it was already extended once five years ago), but US President Donald Trump has been cavalier, saying “If it expires, it expires.”

One reported explanation for the US stance is its unhappiness that China is not included in the formal architecture of arms control. Yes, China possesses the world’s third-largest and fastest-growing nuclear arsenal, but its desire to achieve parity with the US and Russia means it won’t sign any pact limiting it to second-class status.

Moreover, China, thinking about Taiwan, may well believe that a principal reason the US has not directly come to Ukraine’s defence is respect for Russian nuclear strength. But there is a strong case for bringing China into arms control a decade hence — and a reasonable chance of doing so.

In the meantime, the non-extension of New START, however unfortunate, is not the end of the world. Neither the US nor Russia wants a new, costly and dangerous arms race. Yes, there will be some modernization and expansion of arsenals, but it is quite possible a degree of transparency, signaling, and even stability will remain in place — and that a new, formal pact will ultimately be negotiated.

Interestingly, limiting the so-called vertical proliferation of existing nuclear-weapons countries — the expansion of existing arsenals — might not be the biggest challenge we face in the nuclear realm. Of course, it is worrisome in cases such as North Korea, India, and Pakistan, India’s arch-rival, because the conditions that have underwritten US/Soviet and US/Russian deterrence will not be easily replicated.

But arguably more troubling is horizontal proliferation: additional countries seeking to join the nine countries that currently comprise the nuclear club: the five (China, France, Russia, the UK and the US) formally recognised as “Nuclear-Weapons States” under the Nuclear Non-Proliferation Treaty, and Israel, India, Pakistan, and North Korea.

One would-be nuclear-weapons state is Iran. Israeli and US military strikes last year set Iran’s program back but did not reduce its ambitions. On the contrary, the inability to deter the attacks may well have increased Iran’s determination to press ahead.

It remains to be seen what the current talks underway in Oman or quite possibly further military action can accomplish. It is essential that Iran’s ambitions continue to be frustrated, as a nuclear-armed Iran might be more aggressive in its use of proxy forces throughout the region. And it would almost certainly prompt several countries in the region, including Türkiye, Saudi Arabia, and Egypt, to develop or acquire nuclear weapons of their own. The prospect of the world’s least stable region bristling with nuclear weapons is chilling.

For countries in Europe and Asia, two other factors are increasing their interest in nuclear weapons. One is concern about the threats posed by Russia, China, and North Korea. Russia has initiated a brutal war of aggression against Ukraine and has talked menacingly about using nuclear weapons and altering the political map of Europe. North Korea has never given up its aim of gaining control over the entire Korean Peninsula. China seeks to assert its control over Taiwan and its primacy in the region.

Growing concern about the ambitions, intentions, and capabilities of countries that seek fundamental changes to existing geopolitical arrangements dovetails with increasing doubts about whether the US will continue to provide deterrence against such threats.

Alliances have been a successful nonproliferation tool for decades, but the Trump administration has called into question US commitments. The alternative to dependence on the US for many — for South Korea and Japan in Asia, and for any number of countries in Europe — will be nuclear self-reliance.

The main risk is that a country developing or acquiring nuclear weapons might provoke a pre-emptive attack by a neighbour that is not prepared to see a perceived adversary become so threatening. And even if such a transition can take place without leading to war, small nuclear forces may invite an attack in a crisis — or their early introduction (“better to use them before you lose them”) before they are attacked and destroyed.

We need to alter our thinking about nuclear weapons. We have grown too comfortable with them. The time to become uncomfortable has arrived.

This article was first published by Project Syndicate. Views expressed in opinion pieces do not necessarily reflect the position of Novaya Gazeta Europe.