NATO without Article 5
A cold reading: what remains of the alliance if its central clause is treated as ambiguous.
In September 2025 NATO lived through the longest sequence of airspace violations on allied territory since the Cold War. In three weeks Poland shot down Russian drones over its own land, Romania tracked a drone for fifty minutes without firing, Estonia had three MiG-31s inside its airspace for twelve minutes and Denmark closed airports twice. The institutional result was a statement reaffirming that Article 5 is “unwavering” and no invocation of it at all.
That is the designed behaviour of an alliance that decided decades ago to keep ambiguous what exactly triggers the central clause — and that is now discovering the cost of keeping that ambiguity in public.
Article 4 as a pressure valve
The European response to every incident followed the same script: consult, do not escalate. Poland invoked Article 4 on 10 September 2025, after between 19 and 21 drones entered its airspace on the night of 9 to 10. Four were shot down by Polish F-16s and Dutch F-35s, with Italian AWACS and German Patriot support — the first time in the alliance’s history that allied fighters engaged targets inside allied airspace.
Romania, on 13 September, chose differently: it tracked the drone that entered near the Ukrainian border, did not open fire because of collateral risk and summoned the Russian ambassador. Estonia, on 19 September, called the violation “totally unacceptable” and requested Article 4 consultations — the third country in two weeks to reach for the mechanism.
Article 4 is the instrument built for this: mandatory consultation with no commitment to respond. It gives governments something their publics accept — a meeting, a condemnation, a statement — and avoids the question nobody wants to answer out loud: what would constitute an armed attack.
The country that chose not to consult
The most instructive case is Denmark’s, because there the ambiguity ran both ways. On 22 September 2025 drone sightings closed Copenhagen airport for nearly four hours, with at least 35 flights diverted, and Oslo’s airport the same night. On the 24th and 25th, Aalborg — which also serves as a military base — and Billund were closed. Prime Minister Mette Frederiksen called it the most serious attack on Danish critical infrastructure to date and said Russian involvement could not be ruled out.
And yet Denmark did not invoke Article 4. On 26 September foreign minister Lars Løkke Rasmussen explained why: the article has been triggered nine times in the alliance’s history, twice in the preceding weeks, and there was no reason to do it — adding that Copenhagen was not “in the situation where we can attribute what we saw to anyone in particular”.
That is the precise point where a cold reading begins. A country whose airspace and airports were shut chose not to escalate because it could not name the author. Attribution of responsibility, which deterrence doctrine treats as a technical detail, turned out to be the decisive variable: without a named author, there is no article to invoke.
Article 5’s ambiguity was always presented as a deterrent strength. Once incidents stopped being exceptions, it started working — in the opposite direction — as comfort for those who do not want to respond.
The answer that exists, and what it does not solve
What NATO built instead was posture, not clause. On 12 September 2025 it launched Eastern Sentry, a reinforced surveillance activity along the entire eastern flank with no end date, adding fighters, air defence systems, surveillance aircraft and frigates.
Allied Air Command described the shift in terms worth quoting as a confession: a transition “from an air policing mindset to an air defence mindset”, acknowledging there is no silver bullet against airspace violations. Translated: the alliance has accepted that it will keep intercepting.
The 2026 incident list shows the pattern operating rather than theorised. On 15 September 2026 Italian fighters shot down a drone over Lithuania that had entered from the Belarusian side — the first time a drone was downed in Lithuanian airspace — while Denmark accused Russia of firing flares at one of its helicopters in international waters. Copenhagen again declined to invoke Article 4, saying that would require a more direct attack on Danish territory.
What remains
The Ankara Declaration of July 2026 reaffirmed the usual formula — “one for all and all for one” — and created no new trigger mechanism and no objective criteria for use. The weight shifted to spending and industrial output. NATO itself records that 17 allies are expected in 2026 to meet the 1.5% of GDP guideline, well ahead of the 2035 deadline agreed in The Hague.
And Secretary-General Mark Rutte said, four days before this edition, what the institution thinks about the central question: “We will never talk about what exactly triggers Article 5. That ambiguity exists, and it will remain.” The alliance treats the undefined as policy, not as a gap.
The consequence nobody can date is this: a guarantee whose triggering remains deliberately undefined can keep deterring a rational adversary while, at the same time, ceasing to organise the policy of those who rely on it. That is what already shows in European statements and in the spending maths. On the day an incident demands a public reading of the clause, the text will not help — and the decision will have to be taken without it.