What is this defense plan B that the European Union is currently developing?

Facing American uncertainties and geopolitical tensions, the Twenty-Seven are turning to a little-known mechanism of the European treaty: Article 42.7. An emerging tool, but potentially decisive. In Brussels and European capitals, doubt is creeping in. Donald Trump’s outspoken criticism of NATO has revived a lingering concern: will the United States remain a reliable ally in times of crisis? It is in this climate of uncertainty that on Thursday, April 23, the Twenty-Seven decided to explore more seriously a mechanism widely known to the public: Article 42.7 of the Treaty on the European Union. According to Cypriot President Nikos Christodoulides, whose country recently hosted informal discussions, the European Commission has been tasked with developing a “detailed operational plan” specifying the modalities for activating this clause in the event of aggression.

But what exactly does this provision entail? Article 42.7 imposes on member states “an obligation of aid and assistance by all the means in their power” when a Union country is the victim of armed aggression, whether from a state or non-state actor. Unlike Article 5 of NATO, this European mechanism stands out for its flexibility: each state retains a margin of appreciation regarding the nature of its support — military, logistical, financial, or humanitarian.

Yet long perceived as an asset, this flexibility now appears as a vulnerability. “We are in the process of designing a user’s manual for this mutual assistance clause,” explained European Council President António Costa, as cited by The Guardian. In practice, Article 42.7 has only been activated once, by France after the November 13, 2015 attacks. Paris had sought support from its partners to ease its external commitments and redeploy its forces domestically. The pragmatic European response resulted in an increase in contributions from several member states to international operations.

However, if it worked, this experience never led to a clear doctrine. Hence the current questions. “If France were to activate Article 42.7 today, which countries would respond first? and in what form?” asks Nikos Christodoulides. The future European pact will have to provide concrete answers to these questions.

A recent episode has contributed to reviving interest in this clause. At the start of the conflict in the Middle East, a drone attack on a British base in Cyprus prompted a swift mobilization of several European states. According to António Costa, Greece, France, Italy, Spain, and the Netherlands deployed military assets to support the rule. A sort of dry run, even though the clause was not formally activated.

For Cyprus, which is not a NATO member, this European tool holds particular strategic importance. But elsewhere, some states remain cautious, mindful of not weakening the Atlantic Alliance. Officially, Brussels is treading carefully: it is not about replacing NATO but complementing it. “The Alliance remains the cornerstone of collective defense,” recalls a European official quoted by The Guardian. However, the EU has other tools — sanctions, financial aid, civilian coordination — that can bolster the overall response in a crisis.

Nevertheless, the ongoing reflection marks a turning point. For the first time, the European Union is seriously considering structuring an autonomous response to aggression. Simulation exercises are planned in the coming weeks to test different scenarios for activating the clause.

This resurgence of interest in European strategic autonomy is intertwined with the American political context. Donald Trump’s recent characterization of NATO as “very disappointing” and his stated intention to withdraw the United States from the Alliance have acted as a wake-up call. Even Prime Minister Donald Tusk, typically close to Washington, now openly questions in the Financial Times: “The most important question is whether the United States will be as loyal as our treaties envisage.” At the same time, tensions have arisen over the refusal of some European countries, notably Spain, to support the American intervention in Iran. Pedro Sánchez reaffirmed his country’s loyalty to NATO while denouncing “the failure of brute force in the Middle East” and calling for respect of international law.