With every bomb dropped, ship seized and blood-curdling threat of annihilation, Donald Trump increases Iran’s incentive to reject his “grand bargain” peace deal and sprint instead to acquire nuclear weapons for future self-defence. Justifying his declaration of war on 28 February, Trump claimed that Iran – and primarily its nuclear programme – posed an “imminent threat”. But Iran does not possess nukes. The US and Israel do.

US intelligence chiefs and UN inspectors agree there’s no firm evidence that the regime, while developing its technical capabilities and keeping political options open, has built, or ever tried to build, a nuclear weapon since at least 2003, when a covert scheme was exposed. But after Trump’s second unprovoked attack in a year, and his vow to bomb Iranian civilisation back to the “stone ages”, that is very likely to change.

It’s increasingly difficult to argue with the view, attributed to the hardline Islamic Revolutionary Guard Corps generals now running Iran, that nukes are the only sure way of deterring future onslaughts. The US and Israel have twice struck without warning, in the middle of diplomatic negotiations. Even if a peace deal were agreed, Iranians know the ever-vengeful Trump and Benjamin Netanyahu cannot be trusted. The US-Israel axis could sustain its aggression for years to come.

Trump’s focus on “obliterating” Iran’s nuclear programme is as woefully wide of the mark as any misdirected US Tomahawk cruise missile. Indigenous nuclear knowhow cannot be easily bombed away, no matter how many scientists Israel kills. And in any case, Tehran does not necessarily need to reconstitute the capacity and skills required to build nuclear weapons at home. It may be able to buy them off the shelf abroad.

North Korea, a longtime ally, would be the most likely source, while help from Vladimir Putin’s Russia (already collaborating on nuclear energy projects) cannot be entirely ruled out. Kim Jong-un, Pyongyang’s dictator, has steered clear of the war so far. But just as he covertly sent troops to assist Putin in Ukraine, he could yet secretly step in to arm Tehran. On nuclear proliferation, Kim has form.

Iran has joined a growing number of non-nuclear armed countries that have suffered grievously at the hands of domineering nuclear powers. In 1994, Ukraine surrendered its nukes in return for what turned out, when Russia first attacked it in 2014, to be valueless western security assurances. Iraq’s regime, lacking a nuclear deterrent, succumbed to US invasion in 2003. Would Trump have attacked Venezuela in January had it been nuclear-armed?

If the acknowledged nuclear weapons states honoured their 1968 Nuclear Non-Proliferation treaty (NPT) obligation to reduce and ultimately eliminate their nukes, others might feel less need of a nuclear shield. But they persistently break their word. Increasingly, the US and Russia abuse their dominant position – abuses that the NPT was specifically designed to prevent. Israel (unlike Iran) never signed the treaty.

Trump’s alarmingly irrational, impulsive and threatening behaviour creates uncertainty and insecurity by itself. But his militarism also fuels global nuclear weapons proliferation. The US is spending billions modernising its arsenal. Russia, North Korea, France and the UK are doing likewise, while China is rapidly, hugely expanding its forces. Yet Trump has refused to renew a series of cold war arms control treaties.

He trashed Barack Obama’s European-backed 2015 nuclear deal with Iran, a foolish decision that has led directly to today’s confrontation. On the first day of the war, Iran’s supreme leader, Ayatollah Ali Khamenei, was targeted and killed. His binding fatwa expressly forbidding development of an Iranian bomb probably died with him.

Regarding Iran, Trump and Netanyahu labour under two fundamental misconceptions. Even if some form of cold peace is eventually established, Iranians will neither forgive nor forget atrocities such as the Minab school massacre, the wanton destruction visited on their country, and Washington’s diplomatic betrayals – whether or not the current regime remains in power. The “Iran threat” will persist. Second, Tehran still has options over which the US and Israel, despite military superiority, have no control.

Sanctioned, ostracised North Korea offers a possible template for Tehran. The Pyongyang regime originally developed its own atomic weapons using hidden market technology obtained from Pakistan. The Kim dynasty later made nuclear-related transfers to Bashar al-Assad’s Syria. It currently sells ballistic missiles to, among others, Iran and Russia.

It’s speculation at this point, but who’s to say Kim will not provide Iran with complete nuclear warheads? Or if that is too risky, he could supply highly enriched uranium, warhead designs and expertise in return for oil, suggested Mark Fitzpatrick, an International Institute for Strategic Studies non-proliferation expert and former senior US diplomat. If Kim did so, who would know and who could stop him?

Kim has grown increasingly emboldened since the failure of Trump’s embarrassing first-term charm offensive. Ignoring White House signals about renewed contacts when Trump visits Beijing next month, the North Korean leader ostentatiously test-fires new missiles, taunts South Korea and Japan, and stresses closer ties with China, Russia and Belarus. Speaking in March, he said US aggression in Iran “proved” North Korea was right to develop a nuclear deterrent. Tehran has surely heard that message.

If Kim is wrong, then why exactly does Trump treat North Korea so differently from Iran? After all, both countries menace their neighbours and embrace anti-western alliances, both are authoritarian regimes oppressing their citizens, and the North Korean nuclear threat is demonstrably genuine. The reason for the double standard seems obvious. Even Trump is not stupid enough to attack a nuclear-armed state.

The way Trump’s and Putin’s bellicose behaviour is legitimising arguments favouring the possession of nuclear weapons is prospectively disastrous for global non-proliferation efforts. If Iran does seek to acquire nukes to defend itself, will Saudi Arabia, Egypt and Turkey follow? And that’s just in the Middle East. Like Ukraine, the Iran war also provides cover and precedent for other nuclear weapons states if they, too, decide to attack non-nuclear-armed countries. Might China follow suit in Taiwan? Given Iran’s fate, should Taipei rush to acquire nukes? Should Japan and South Korea?

Little wonder that an air of gloom hangs over the five-yearly NPT review conference, which opens in New York on Monday. Its challenges include ubiquitous nuclear weapons modernisation and expansion programmes; the collapse of arms control diplomacy; resumed nuclear testing; and what the Arms Control Association calls “rising nuclear dangers” and proliferation risks. “The idea of ‘global zero’, or a world without nuclear weapons, is seen to be steadily eroding,” a House of Commons Library research briefing warned this month.

This is no made-up story with which to scare the children. It’s real. Since invading Ukraine, Russia has repeatedly threatened to use nuclear weapons. So far, fortunately, it has not. In recent weeks, as Trump flailed in Iran, there was a flurry of reports, later denied, that the US, too, might resort to nukes. Sabre-rattling or not, such threats are becoming way too familiar. If a just and reasonable negotiated path can be found out of the present morass, Iran and similarly vulnerable middle-ranking countries may be persuaded to continue to forego nuclear weapons. But if lawless aggression by domineering “might is right” nuclear-armed powers spreads unchecked, the old cold war nightmare of mutually assured destruction will become today’s waking reality.

• Simon Tisdall is a Guardian foreign affairs commentator