THE Treaty on the Prohibition of Nuclear Weapons marks a major step forward for the international disarmament movement.

Nuclear weapons are, for the first time, illegal under international law. Powerful countries break international law all the time, of course, and nuclear-armed states have adopted a contemptuous attitude to the treaty from the start. 

When the UN general assembly voted on the treaty (it passed 122 votes to one, with one abstention) nuclear weapons states, as well as the members of the nuclear-armed US-led Nato alliance, declined even to abstain, in case participating in the vote be read as giving the outcome any legitimacy.

But the clear global majority call for the elimination of nuclear weapons undermines the the nuclear states’ claims to be guardians of international law and — like the US’s endless wars — underlines the hypocrisy of US allies who claim to police a “rules-based international order” when they flout all rules not written by themselves — and frequently enough flout those too.

It must be used to rebuild popular mass movements for nuclear disarmament that highlight the urgency of an issue sometimes seen as a cold war throwback.

Much of the framework of international disarmament treaties painstakingly built up by the United States and Soviet Union has been ripped up by the Donald Trump administration.

The demise of the Intermediate Nuclear Forces (INF) treaty could see zones of superpower rivalry bristle again with medium-range nuclear warheads, while the abolition of Open Skies reinforces mutual suspicion and raises the risk of miscalculation in a game with apocalyptic stakes.

Under Trump the US built smaller-yield “tactical nuclear warheads” cited as giving the holder a battlefield advantage. Last year the US confirmed it had started arming submarines with these. 

As usual the move is justified as part of a game of bluff and double-bluff: if a country fears the US would be more likely to fire a smaller nuclear weapon, its behaviour will be accordingly cowed without the US actually doing so.

But the reason an adversary would consider it more likely is because it is more likely, while the US deployment of such missiles gives other states an incentive to get them too. The horrific consequences of normalising the concept of a “limited” nuclear war are obvious.

The Trump presidency is mercifully over, but there is a real risk that even governments alarmed by Trump settle for “two steps back, one step forward” and a new normal that is closer to the precipice.

Moscow has offered to extend the last remaining nuclear treaty between it and Washington — the New Start agreement limiting the number of active nuclear warheads they hold — and it is likely the Joe Biden administration will agree. 

It is much less clear whether efforts will be made to restore the INF treaty or Open Skies and it seems vanishingly unlikely that the US will ditch its “tactical” warheads unless under sustained domestic and international pressure to do so.

In most foreign policy areas, Biden’s pick for secretary of state Antony Blinken indicates he would continue Trump’s line, from treating Jerusalem as Israel’s capital, through recognising the unelected nobody Juan Guaido as Venezuelan president to maintaining a dangerously confrontational approach to China.

The last is rapidly escalating into a cold war in which channels of communication and compromise are disappearing, while Nato continues to harass Russia with major military exercises on its borders.

This is a context where the collapse of arms control mechanisms makes catastrophic war more likely. 

Resistance to it will not come from “official” politics, where Tories and Labour egg each other on to new heights of aggression internationally and both treat nuclear disarmament as a peacenik fantasy.

It will have to come from below, through increased support for the Campaign for Nuclear Disarmament and a stronger peace movement that those in power cannot afford to ignore.