NATO’s Twilight: How the Iran War Could Unravel the Western Alliance

The North Atlantic Treaty Organisation (NATO) may become a collateral casualty of the US-Israeli war on Iran. What began as transatlantic friction over defence spending has become a slow-burning fuse that threatens to blow up the alliance.

On Friday (April 24), Reuters reported that an internal email in the Pentagon outlined options for the US to punish NATO allies for failing to support US operations against Iran. The email detailed policy options prepared by Elridge Colby, the Pentagon’s top policy adviser, who suggested suspending Spain from the alliance and even reviewing support for UK’s claim to the Falklands islands in the southern Atlantic.

On April 1, President Trump was asked whether he might reconsider NATO membership once the war concluded. His reply was unsparing: “Oh yes, I would say [it’s] beyond reconsideration. I was never swayed by NATO – I always knew they were a paper tiger, and Putin knows that too, by the way.” He was not just venting frustration, the words seemed to have a ring of a settled conclusion.

For the present, the Colby email does not suggest that the US withdraw from NATO, nor does it propose closing bases there. But it could involve a reduction of US forces in Europe. And as for Spain, there is no provision in NATO’s Founding Treaty for suspending any member.

Illustration: Pariplab Chakraborty.

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Trump’s anger with NATO is not new, but it has found fresh fuel in the alliance’s response – or rather, its refusal to respond – to the Iran campaign. The principal NATO members not only declined to participate militarily; several went further, blocking the use of their airspace for missions targeting Iranian territory. When Washington called on allies to help open the Strait of Hormuz last month, it was bluntly rebuffed.

Should Trump pull the trigger on withdrawal, he will, however, face a statutory obstacle: in 2023, Congress approved legislation requiring either a two-thirds majority in the Senate or separate congressional legislation before any president could unilaterally exit the alliance. That is a high bar, but Trump has never been shy about testing institutional limits.

The immediate diplomatic fallout is already reshaping European politics. British prime minister Keir Starmer, subjected to weeks of personal derision from Washington over London’s refusal to support the Iran venture, has signalled a decisive pivot toward the European Union. He described a closer partnership with Europe as essential for “this dangerous world that we must navigate together,” framing the shift as a matter of Britain’s “long-term national interest.” The language is carefully chosen – and consequential. A rapprochement with Brussels would represent a partial undoing of Brexit. The residue of that 2016 decision – particularly in trade and regulatory alignment – will complicate any swift deepening of defence ties between Britain and the EU.

French president Emmanuel Macron has emerged as the most withering European voice. Now a target of Trump’s personal comments, Macron has chosen this moment to say plainly what others have only whispered. He has bluntly noted that this was not a NATO operation, but one “which the Americans decided on with the Israelis.”

He derided Trump’s constant chatter, saying “the opposite of what we said the day before.” He noted that alliances like NATO depended on “what is unspoken – meaning the trust behind them.” He went on to add that “If you create doubt every day about your commitment, you hollow it out.”

Even Georgia Meloni of Italy, the only European leader to be invited for Trump’s second inauguration and considered close to him has been clear in her opposition to the war against Iran. “When we don’t agree, we must say it. And this time, we do not agree,” she has said. Italy refused to allow US bombers to refuel at a military base in southern Italy.

The estrangement predates this crisis. Trump’s pursuit of Greenland has roiled ties between Europe and the US with the US threatening a 25% import tax on European nations unless they comply. Last year, vice president J.D. Vance warned of an “enemy from within” menacing Europe – a civilisational critique framed around migration, democracy, and free speech. Trump’s 2025 National Security Strategy spoke of Europe facing “civilisational erasure.” These are hardly the words of an ally. The war on Iran has simply accelerated a divergence that was already underway.

Were the United States to exit NATO formally, the consequences for European security would be severe and structural. For decades, the continent has literally outsourced its defence to American power – troops on the ground, military bases from Poland to Italy, and critical force multipliers that European militaries largely lack: satellite intelligence, heavy-lift transport, in-flight refuelling, advanced missile defence. The United States currently accounts for roughly 61 percent of total NATO defence spending. It was this factor that shaped the Trump critique of European “free loading”.

Under Trump’s pressure European nations have been increasing their defence budgets, but a full American withdrawal would demand an even steeper price. Spending more on defence means less on social welfare, infrastructure, and the green transition that European governments have promised their electorates. The politics of rearmament, in peacetime, is never easy.

Ramifications would not stop at Europe’s borders

Minus NATO Europe would have to revert to its founding Treaty of Lisbon to shape a new security strategy. Its Article 42.7 obliges member states to provide military, humanitarian and financial aid to other members in case of attack. But this has been meant to complement NATO and has been used just once, by the French in response to the November 2015 terror attacks. But a lot more would have to be done to create a viable defence system for Europe to replace NATO.

A credible European defence capability would require, at minimum, meaningful progress toward a unified command structure – a project that has been gestating for decades and remains fiercely contested. Hungary’s Orbán government had demonstrated its willingness to obstruct EU consensus on security matters. Forging a coherent military posture across twenty-seven states with divergent interests and threat perceptions is not simply a technical problem; it is a political one of the first order.

And the ramifications would not stop at Europe’s borders. American alliance architecture is a system, not a collection of independent bilateral arrangements. A NATO exit would reverberate across East Asia, raising uncomfortable questions for Japan, South Korea, and Australia. If Washington is willing to abandon its oldest and most institutionalised alliance in a fit of pique over airspace rights, what assurance remains for partners in the Indo-Pacific who have constructed their security strategies around American reliability?

The deeper loss, if NATO fractures, will be harder to quantify than spending percentages or basing rights. It is the loss of a shared assumption — that the post-1945 order, however imperfect, was worth defending collectively. That assumption has been the key pillars of Western security for eighty years. Trump is not just questioning the architecture. He is kicking at the foundations.

Whether Congress acts as a brake, whether European leaders can improvise an alternative, whether the alliance limps on in diminished form with Trump simply withdrawing troops from Europe and declaring that the US will not uphold Article V remains to be seen. What is evident, however, is the real damage done to the alliance.

The writer is a distinguished fellow with the Observer Research Foundation in Delhi.

This piece was first published on The India Cable – a premium newsletter from The Wire – and has been updated and republished here. To subscribe to The India Cable, click here.

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