The nuclear issue has once again occupied the center of world politics. Although the specter of nuclear proliferation never went away, it remained hidden for decades thanks to a functional and predictable world order, underpinned by American hegemony, a strong NATO, and credible arms control regimes. But this order is now under unprecedented pressure, and the US-Israeli war against Iran is just the latest proof of this. How can we preserve nuclear restraint in a world where the architecture of restraint is crumbling?
The beginning of the nuclear age represented a radical change in strategic thinking. Until then, military power was measured by the ability to win wars, which was tested on the battlefield. But the goal of nuclear weapons was deterrence, not victory.
Nuclear weapons did not end conflicts. The Cold War remained violent, dangerous, and morally depraved. The proxy wars intensified and people lived in fear. Nuclear weapons raised the stakes of conflicts, and mutually assured destruction helped avoid direct war between superpowers. Deterrence worked not because it made leaders virtuous, but because it made escalation suicidal.
That grim logic is still relevant, but its context has changed. While the Cold War was fundamentally bipolar, the current nuclear order is multipolar. China joins the United States and Russia as a great nuclear power. Although China’s arsenal remains smaller, the US Department of Defense projects it could exceed 1,000 operational nuclear warheads by 2030.
The result will not simply be an expanded version of the Cold War. Trilateral deterrence is more unstable than bilateral deterrence. Each great power must calculate not only its balance with adversaries, but also how measures against one affect the other. Arms control becomes more ambiguous and crisis management more complex.
To further complicate matters, there are other nuclear states – the United Kingdom, France, India, Israel, North Korea and Pakistan – each with their own nuclear doctrine, geography, fears and political imperatives. Their arsenals are smaller, but the danger they represent is not. A nuclear confrontation on the Korean peninsula or between India and Pakistan would not only constitute a major regional tragedy, but would affect broader alliances, disrupt global markets and supply chains, and upend the calculations of great powers.
But perhaps the most dangerous factor in the emerging nuclear order are the states that aspire to remain on the threshold (threshold states). The risk is not only that more states build large arsenals, but that some acquire just enough nuclear capability to believe they can intimidate their neighbors, deter foreign intervention, or survive conventional defeat. A few nuclear weapons can be enough to transform a regional crisis into a global crisis.
This raises the stakes in negotiations to end the war in Iran. An agreement that achieves an immediate military de-escalation and reopens the Strait of Hormuz could be diplomatically useful. But if it does not include a clear deal on Iran’s nuclear program, the lesson — not just in Tehran, but also in Turkey, Saudi Arabia, South Korea and Japan — could be that proliferation is a valid strategy.
Europe is also attentive. NATO’s collective defense clause remains the cornerstone of European security, but it is not an automatic mechanism; It must be activated through political decisions. The more European NATO countries doubt that the United States will fulfill its commitment to come to their defense, the more they will protect themselves, through strengthening national capabilities, special bilateral guarantees and alternative nuclear deterrents.
This is not a hypothetical possibility. While Polish President Andrzej Duda has called for the deployment of US nuclear weapons on Polish territory – in an attempt to obtain greater guarantees that the US nuclear umbrella can be counted on – Prime Minister Donald Tusk has stressed the importance of autonomy in nuclear deterrence. Furthermore, German Chancellor Friedrich Merz has pushed forward debate on a shared European nuclear umbrella, largely backed by France and the United Kingdom.
France certainly seems to agree with the idea. In March, French President Emmanuel Macron outlined an “advanced deterrence” doctrine, which would encompass the country’s European allies. Belgium, Denmark, Germany, the Netherlands, Greece, Poland, Sweden and the United Kingdom have already agreed to participate in the strategy, supporting France’s nuclear deterrent with their conventional forces.
But the so-called French nuclear parapluie has fundamental limitations: it is selective, sovereign and reversible. It does not cover all member states of the European Union; leaves some countries (like Spain) outside the closest circle; and keeps decision-making on nuclear matters exclusively in the hands of France. Macron’s rhetoric does not point to the emergence of a true European nuclear deterrent, but rather an attempt to disguise burden redistribution in the language of strategic autonomy.
Ultimately, there is no substitute for the American security guarantee. But Europe must do its part to ensure that this guarantee remains politically sustainable. To that end, rather than coming to the upcoming NATO summit in Ankara with anxiety disguised as outrage, European leaders should arrive with a commitment to strengthening the Alliance’s European pillar.
This means expanding its conventional capabilities, improving its air and missile defenses, increasing its arsenals, improving its intelligence and surveillance capabilities, and increasing its contribution to deterrence below the nuclear threshold. The greater Europe’s conventional capabilities, the less the results will depend on the United States’ willingness to risk nuclear escalation.
Crucially, this approach would also reduce pressure toward proliferation, which would be good news for the United States. The last thing the country wants is a world in which every uneasy ally or regional power concludes that only nuclear weapons can guarantee its security. American ambiguity can be useful at the margin; American abandonment would be fundamentally destabilizing.
The nuclear age began with the realization that victory could mean catastrophe. That risk remains as serious as ever, but the institutional framework that mitigated it has been deeply eroded. The task now is to prevent the pursuit of deterrence from giving way to proliferation. For Europe, this means maintaining US commitment, developing conventional capability, preserving NATO’s credibility, and upholding strategic restraint.
Ana Palacio was Minister of Foreign Affairs of Spain and Senior Vice President and General Legal Counsel of the World Bank Group; She is currently a visiting professor at Georgetown University.
Copyright: Project Syndicate, 2026.
