The war with Iran that President Donald Trump launched three months ago has become his latest cudgel against the North Atlantic Treaty Organization—and this time, European capitals fear he might actually follow through on his threats to walk away.

In a series of heated phone calls with NATO Secretary General Mark Rutte over the past two weeks, Trump has repeatedly demanded that European members either deploy forces to support American operations in the Persian Gulf or accept what he calls a "fundamental reassessment" of U.S. commitments to the alliance, according to three senior European officials briefed on the conversations.

The ultimatum represents the most serious challenge to NATO's existence since its founding in 1949. Unlike Trump's first-term complaints about defense spending—which European leaders largely dismissed as bluster—this confrontation involves an active shooting war where American service members are dying, and where European governments have explicitly refused to participate.

"He's not just complaining about burden-sharing anymore," said a senior German defense official who spoke on condition of anonymity to discuss sensitive diplomatic matters. "He's asking us to choose between our principles and the alliance itself."

A War Europe Won't Join

The current crisis stems from fundamental disagreements about the Iran conflict, which began in January when U.S. forces struck Iranian nuclear facilities following what the administration characterized as an imminent threat. European intelligence agencies disputed that assessment, and every major European NATO member—including the United Kingdom, France, and Germany—declined American requests for military support.

France's President Emmanuel Macron went further, publicly stating that the U.S. strikes violated international law. That comment, according to two people familiar with the exchange, prompted Trump to suggest in a subsequent call that France should "maybe think about going it alone" without American security guarantees.

The refusal to back the Iran operation stands in stark contrast to the near-universal European support the United States received after the September 11, 2001 attacks, when NATO invoked Article 5—its collective defense clause—for the first and only time in history. European forces fought alongside Americans in Afghanistan for two decades, suffering thousands of casualties.

But the Iran war carries different moral weight for European leaders. Public opinion across the continent runs strongly against the conflict, with polling in major NATO countries showing opposition ranging from 68% in the United Kingdom to 81% in Germany. Governments that joined American operations would likely face political catastrophe at home.

"Afghanistan was a response to an attack on allied soil," explained a senior British official. "This is a war of choice that we believe was unnecessary and counterproductive."

The Greenland Gambit Returns

Complicating the NATO crisis is Trump's renewed fixation on acquiring Greenland, the autonomous Danish territory he first attempted to purchase during his previous presidency. According to as reported by the New York Times, the president has explicitly linked the two issues in recent conversations with Danish Prime Minister Mette Frederiksen.

In one particularly contentious exchange last week, Trump reportedly told Frederiksen that Denmark's refusal to even discuss selling Greenland—combined with its failure to support U.S. operations against Iran—raised "serious questions" about whether America should continue defending Danish territory under Article 5.

The Greenland obsession reflects Trump's transactional view of international alliances. He has long viewed the island's strategic location and mineral resources as valuable American assets that Denmark unfairly controls. The fact that Greenland's 57,000 residents have repeatedly expressed no interest in becoming American territory appears not to factor into his calculations.

Danish officials have responded with barely concealed fury. "Greenland is not for sale, has never been for sale, and will never be for sale," Frederiksen said in a statement. "Linking this fantasy to our NATO obligations is beneath the dignity of the alliance."

Rutte's Impossible Mission

Mark Rutte, the former Dutch prime minister who became NATO Secretary General last year, finds himself navigating an almost impossible situation. He must somehow preserve alliance unity while mediating between a U.S. president threatening to abandon collective defense and European governments that view the Iran war as illegitimate.

Rutte has spent much of the past month shuttling between Washington and European capitals, attempting to craft compromises that might satisfy Trump without requiring European governments to endorse military operations they oppose. Options under discussion reportedly include increased European naval patrols in the Mediterranean to free up American ships for the Gulf, or expanded European defense spending to offset the costs of U.S. Iran operations.

But none of these proposals appear to satisfy Trump, who associates say believes European "betrayal" on Iran justifies a wholesale rethinking of American security commitments. The president has privately told advisers that NATO has become a "protection racket" where the United States assumes all the risks while European allies pick and choose which American wars to support.

The Stakes for Western Security

The potential collapse or severe weakening of NATO would represent a seismic shift in global security architecture. The alliance has served as the cornerstone of Western defense for more than seven decades, deterring Soviet and later Russian aggression while providing a framework for military cooperation across dozens of democracies.

European defense officials worry particularly about the signal that American withdrawal would send to Moscow. Russia's war in Ukraine—now in its fifth year—has already tested NATO's resolve. A U.S. exit or even significant drawdown would likely embolden Russian President Vladimir Putin to apply further pressure on alliance members in Eastern Europe.

"If Trump actually follows through, we're talking about the end of the post-World War II security order," said a senior Polish defense official. "Putin would view it as a green light."

Yet European governments also face domestic political realities that make supporting the Iran war nearly impossible. The conflict has already claimed more than 2,000 American lives and shows no clear path to resolution. European publics, still scarred by the Iraq War's aftermath, have little appetite for another Middle Eastern military adventure.

The Path Forward

As the crisis deepens, some European officials have begun quietly discussing contingency plans for a NATO without full American participation—or possibly without America at all. These conversations remain preliminary and highly sensitive, but they reflect growing acknowledgment that Trump's threats may not be empty.

The European Union's nascent defense initiatives, long stalled by bureaucratic obstacles and national rivalries, have taken on new urgency. France has pushed for accelerated development of independent European military capabilities, while Germany debates whether to finally abandon its post-war reluctance to assume a leadership role in continental defense.

For now, Rutte continues his diplomatic efforts, hoping to find some formula that prevents a complete rupture. But with Trump showing no signs of backing down, and European governments unable to reverse course on Iran without political suicide, the coming weeks may determine whether the trans-Atlantic alliance can survive its deepest crisis since inception.

The bitter irony is not lost on alliance veterans: NATO, which was created to deter external threats to Western democracies, now faces its greatest danger from within.