This week marks 25 years since NATO invoked Article 5 of its founding treaty for the first and only time, a decision made in direct response to the September 11, 2001 attacks on the United States. The anniversary arrives as officials in Washington signal a pullback from long-standing commitments to Europe, according to the New York Times, and it has prompted allies to revisit a moment when the alliance’s collective defense clause was activated not for a European member state, but for the United States itself.
The symbolism of that 2001 vote carries new weight this year. NATO was founded in 1949 on the premise that an attack on one member is an attack on all, yet the clause sat unused for more than five decades until the day after the World Trade Center and Pentagon attacks. European governments invoked it not because Europe was under threat, but because an ally across the Atlantic had been struck. Twenty-five years later, European officials are citing that history as they weigh what a reduced American presence in NATO could mean for the continent’s own security, according to the New York Times.
Elsewhere, the anniversary has produced smaller, more personal displays of the same trans-Atlantic connection. Hundreds gathered at the International Peace Garden on the Canada-U.S. border for a ceremony marking the 25th anniversary of the attacks. Organizers described the event as affirming an “unbreakable bond” between the two countries, according to Global News. Held on a remote stretch of prairie straddling Manitoba and North Dakota, the ceremony captured a theme running through this year’s commemorations: allies reaching for reminders of solidarity even as the underlying relationship shifts.
The 2001 decision: NATO’s collective defense clause activated for the U.S.
NATO’s North Atlantic Council invoked Article 5 on September 12, 2001, one day after hijacked aircraft struck the World Trade Center and the Pentagon and crashed in Pennsylvania. It was the only time in the alliance’s history the clause has been triggered, and the only time it has applied on behalf of the United States rather than a European member state. The decision reversed the assumption built into NATO’s founding purpose: an alliance formed to defend Western Europe against the Soviet Union instead moved to defend its largest and most powerful member.
The vote carried practical consequences beyond its symbolism. NATO began surveillance flights over U.S. territory using its Airborne Warning and Control System (AWACS) aircraft, freeing up American assets for operations abroad. European member states also opened airspace, ports, and bases to U.S. forces preparing for the campaign in Afghanistan. The invocation gave Washington a formal claim on collective alliance resources at a moment when the U.S. was organizing a global response to the attacks.
What Article 5 required of European member states
Article 5 does not obligate members to commit troops automatically. It requires each ally to take “such action as it deems necessary,” phrasing that leaves room for individual governments to determine their own contributions. In practice, invoking the clause in 2001 opened the door for European states to support U.S. military action through logistics, intelligence-sharing, and eventually troop deployments to Afghanistan under the NATO-led International Security Assistance Force, established in 2001 and expanded over subsequent years. The clause’s flexible language meant the scale of European involvement varied considerably by country, but the initial invocation itself was unanimous among member states at the time.
Two decades of trans-Atlantic strain since the alliance’s founding moment
The unity of September 2001 did not last. Within two years, the invasion of Iraq split the alliance along lines that never fully healed. France and Germany opposed the U.S.-led campaign, while Britain, Spain, and several Eastern European governments backed it, exposing divisions over how far the post-9/11 consensus extended. The Article 5 invocation had been framed as a response to terrorism; the Iraq war, justified in part on disputed claims about weapons of mass destruction, tested whether that solidarity could stretch to cover a broader war of choice.
Afghanistan proved a longer and more corrosive strain. NATO’s mission there, the alliance’s largest ground operation in its history, ran for nearly two decades before the chaotic U.S. withdrawal in August 2021. European allies, many of whom had committed troops and sustained casualties alongside American forces for years, were given limited notice ahead of the final pullout, according to accounts of the period. The withdrawal left several European capitals questioning how much weight Washington still placed on consultation with allies who had answered the Article 5 call two decades earlier.
Iraq, Afghanistan withdrawal, and the erosion of consensus
Both episodes chipped away at the model of collective decision-making that the 2001 invocation seemed to promise. Iraq showed that invoking Article 5 in a moment of crisis did not guarantee agreement on subsequent military strategy. Afghanistan showed that even sustained, multi-year European commitment could end with a U.S. exit decided largely in Washington. Together, the two conflicts left a residue of skepticism in European capitals about how durable American security guarantees actually are, skepticism that has resurfaced sharply in this year’s anniversary coverage.
European officials confront a new era of American retrenchment
Twenty-five years after the only Article 5 invocation in NATO’s history, European officials are grappling with what the New York Times describes as an era of American retrenchment. The shift is prompting allied governments to reassess assumptions that have underpinned European defense planning since the Cold War: that the United States would remain the anchor of the continent’s security architecture regardless of changes in Washington’s political leadership.
Reactions from NATO capitals as Washington reduces its commitments
The anniversary has become a moment for European governments to publicly recall the depth of the bond formed in 2001, even as they privately recalibrate expectations. That recalibration is not simply rhetorical. It touches defense budgets, troop postures, and the degree to which European capitals believe they can rely on rapid U.S. reinforcement in a future crisis. The Peace Garden ceremony on the Canada-U.S. border, with its language of an “unbreakable bond,” points to one instinct: reaffirm continuity. The tone coming out of European policy circles, as described in the New York Times, points to another: prepare for a relationship that looks different than it did a quarter century ago.
Why the anniversary lands differently amid current U.S. foreign policy shifts
The 25th anniversary would have drawn attention under any circumstances, given Article 5’s singular use in the alliance’s history. But its timing sharpens the message. Coming as Washington signals reduced commitments abroad, the anniversary invites a direct comparison between the moment European allies mobilized fully behind the United States and the current moment, in which the direction of American engagement with Europe is in question. That contrast, more than the historical facts of 2001 alone, has driven renewed attention to the episode this month.
The anniversary also lands amid separate but related debates over America’s overseas footprint. In Japan, for instance, discussions over the long-term U.S. military presence on Okinawa point to a similar recalibration of how Washington’s alliance commitments are perceived. Whether in the Pacific or in Europe, the underlying question is the same: how much can allies count on arrangements built for a different strategic era.
What European leaders are asking of Washington now
European officials are not asking for a repeat of the 2001 invocation, an event tied to a specific attack rather than a general request for reassurance. What they are seeking, based on the tenor of this year’s commemorations, is clarity: a clearer signal of what the United States intends to sustain in Europe going forward, and on what terms. The 25th anniversary of Article 5’s only invocation has become less a celebration of past unity than a marker against which the current state of the alliance is being measured. For European capitals, the next test is not whether they would answer a future call from Washington. It is whether Washington still intends to make one.
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