For seventy-five years, the North Atlantic Treaty Organisation rested on a simple bargain. As NATO’s first Secretary General, Lord Ismay, famously put it, the alliance was designed “to keep the Russians out, the Americans in, and the Germans down.” That bargain is now unraveling—not because of a resurgent Moscow, but because the current occupant of the White House has made its destruction a personal project.

Donald Trump has threatened to withdraw from NATO repeatedly. He has humiliated European allies, questioned the alliance’s mutual defence clause, and demanded they join a military confrontation in the Persian Gulf that most consider reckless and illegal. When they refused, he began talking openly about leaving. Whether he can legally do so is a matter for lawyers. The real question is: what happens to Europe, to Russia, and to American power if he does?

What NATO Was For

NATO was never just a military alliance. As the historian Timothy Sayle argues in Enduring Alliance, it was a political insurance policy against the return of European great-power rivalry and the spread of communism. For Britain, staggering from the loss of India in 1947 and the end of its empire, NATO provided a way to remain Washington’s indispensable partner. For West Germany, it offered rehabilitation and a shield against the Soviet Union. For the United States, as Melvyn Leffler has shown, the alliance was one pillar of a broader national security state designed to protect democratic capitalism and an American-centric global trading system.

The bargain worked. The Cold War ended without a third worldThird World Full Description: Originally a political term—not a measure of poverty—used to describe the nations unaligned with the capitalist “First World” or the communist “Second World.” It drew a parallel to the “Third Estate” of the French Revolution: the disregarded majority that sought to become something. The concept of the Third World was initially a project of hope and solidarity. It defined a bloc of nations in Latin America, Africa, and Asia that shared a common history of colonialism and a common goal of development. It was a rallying cry for the global majority to unite against imperialism and racial hierarchy. Critical Perspective:Over time, the term was stripped of its radical political meaning and reduced to a synonym for underdevelopment and destitution. This linguistic shift reflects a victory for Western narratives: instead of a rising political force challenging the global order, the “Third World” became framed as a helpless region requiring Western charity and intervention. war. But when the Soviet Union collapsed in 1991, NATO faced an existential crisis. Realist theorists like Kenneth Waltz asked: how can an alliance survive without an enemy?

The Expansion Debate

NATO survived by expanding eastward—a decision that remains fiercely contested. In 1990, US Secretary of State James Baker assured Mikhail Gorbachev that NATO would not move “one inch eastward.” As Mary Elise Sarotte documents in Not One Inch, that assurance was specifically about East Germany, not a blanket promise. But Gorbachev believed it. When NATO admitted Poland, Hungary, and the Czech Republic in 1999, followed by the Baltic states in 2004, Moscow felt betrayed.

John Mearsheimer, the leading offensive realist, argues that this expansion was a catastrophic provocation. He has written that Putin considered Ukraine’s potential NATO membership an existential threat and that the West should have understood this. Fiona Hill, who served as Trump’s Russia adviser, offers a different view: Putin’s hostility to the West predates NATO expansion, dating back to his 2007 Munich speech. In her account, Putin had declared war on the post-Cold War order long before any further enlargement.

Both sides have merit. But neither explains the current crisis.

The Trump Earthquake

What makes Trump different is not his scepticism of NATO—presidents from Eisenhower to Obama have complained about European free-riding. It is the combination of unpredictability, personal grievance, and the specific demand he has made of allies.

In early 2020, following the US assassination of Iranian General Qasem Soleimani, Trump asked NATO to invoke Article 5—the mutual defence clause—to support American military operations in the Persian Gulf. European allies, including Britain and France, refused. They argued, correctly, that the Soleimani strike was a unilateral US action, not a response to an attack on a NATO member. Trump responded by threatening to withdraw from the alliance and by publicly ridiculing European defence spending.

This was not a disagreement over burden-sharing. It was a fundamental redefinition of the alliance: not as a collective defence pact but as a tool for US power projection. When Europe declined, Trump took it personally.

Can He Actually Leave?

The legal barriers to unilateral withdrawal are higher than Trump suggests. The 2023 National Defense Authorization Act stipulates that no president may withdraw from NATO without either a two-thirds Senate majority or an act of Congress. But legal niceties may not restrain a president determined to act. As Sophia Besch of Carnegie Europe has noted, the damage is already done: European policymakers no longer assume the US security guarantee is reliable.

Trump has also revealed, with characteristic indiscretion, that US-supplied F-35 fighters and the British Trident nuclear system contain American components that make them operationally dependent on Washington. There is no literal “kill switch”—that is a journalistic shorthand—but the reality is that Britain cannot use Trident without US maintenance and software support. The point is not that Trump would disable allied weapons. The point is that he has signalled he could.

What Collapse Would Mean

If the United States formally withdrew or simply made its commitment incredible, the consequences would cascade.

For Europe: The continent would lose the American nuclear umbrella. France has its own independent deterrent, but it is not a continental defence. European NATO members would need to raise defence spending dramatically, accelerate plans for a joint military force, and decide whether to develop a shared nuclear capability. That would take a decade at best.

For Russia: Contrary to the tankie argument that NATO expansion alone caused the war, a post-American Europe would not be defenceless. Russia is vastly poorer than the Soviet Union, with a smaller population and a degraded military after three years of war in Ukraine. Even without the US, Poland would fight. But a weaker NATO would embolden Putin, potentially leading to further pressure on the Baltic states or Moldova.

For America: Withdrawal would cost the US access to dozens of European bases, intelligence-sharing agreements, and the Five Eyes network. It would devastate the American arms industry, which relies on European purchases of F-35s, missiles, and air defence systems. And it would hand China the greatest strategic gift of the twenty-first century: a divided West.

Conclusion

Ismay’s bargain—keep the Russians out, the Americans in, the Germans down—has held for three generations. It may not survive the fourth. Trump may never formally withdraw. But he has already done something almost as damaging: he has made America’s commitment unbelievable. The world at the end of the 2020s will not resemble the one we entered. And the most urgent question is not whether NATO survives, but what Europe builds in its place.