US President Donald Trump’s rhetoric on everything from punitive tariffs to “ownership” of Greenland has prompted a rethink of Europe’s defense strategy. In Brussels, diplomats, officials and think-tankers have spent much of the past year debating whether the US would still respect NATO’s Article 5 — the pledge that an attack on one signatory is an attack on all — if called upon.
But whether or not NATO’s collective defense clause holds, there is another, lesser-known pledge that binds most European states. Article 42.7 of the European Union obligates member states to provide aid “by all the means in their power” if another EU country is under attack.
What is Article 42.7 and how does it differ from NATO’s Article 5?
In 2009 the Lisbon Treaty added a mutual defense clause under Article 42.7 stating that “if a member state is the victim of armed aggression on its territory, the other member states shall have towards it an obligation of aid and assistance by all the means in their power.”
The article also clarifies that this obligation “shall not prejudice the specific character of the security and defense policy of certain member states,” acknowledging countries whose main defense commitments are shaped by NATO.
Juraj Majcin, security and defense policy analyst at the European Policy Center in Brussels, says the main difference between the EU and NATO mutual defense clauses lies in how support is delivered. The EU provision is largely based on intergovernmental and bilateral assistance, while NATO’s collective defense reflects a broader, more structural deterrence principle.
Former German MP and defense specialist Kristian Klinck argues Article 42.7 is more compelling on paper than NATO’s Article 5 because the requirement to provide help “by all means in their power” is widely interpreted as “to the end of one’s strength.” By contrast, Article 5 allows each NATO country to take “such action as it deems necessary, including the use of armed force,” giving more national discretion.
Both experts stress that assistance under Article 42.7 need not be military. It can include diplomacy, humanitarian aid and financial backing — important for traditionally non-aligned EU members such as Austria, Cyprus, Ireland and Malta.
Has either clause ever been tested?
NATO’s Article 5 has been activated only once: after the 9/11 attacks in 2001. The alliance deployed several radar surveillance aircraft to help patrol US airspace. In total, 830 crew members from 13 NATO countries flew more than 360 missions.
The EU’s Article 42.7 has also been invoked only once — in 2015 after ISIS-led attacks in Paris. Germany and other EU members supported French forces with naval and air assets, but mostly as part of a US-led anti-ISIS coalition.
Majcin cautions that in both cases the clauses were applied to events “they were not designed for.” Klinck agrees, noting that France faced a terrorist attack, not a major military assault, and that Article 42.7 therefore remains largely untested.
Would EU states really defend each other?
Since Russia’s full-scale invasion of Ukraine in 2022, many EU states have boosted NATO defense spending and worked to integrate their military systems. Klinck says Europe still has a long way to go on capabilities, but progress exists: Dutch land forces are fully integrated with German land forces and train and operate together, and there is Dutch-Belgian naval cooperation. If that work continues and leaders act with the spirit shown in Davos when they reacted to Trump’s comments on Greenland, Europe could be up to the task, he says.
NATO chief Mark Rutte delivered a different message: “If anyone thinks here again that the European Union, or Europe as a whole, can defend itself without the US, keep on dreaming.”
Majcin concurs that when discussing Europe’s ability to defend itself without the United States, one should not focus only on a large-scale attack like in Ukraine. He warns that Russia aims to politically undermine NATO, to show Article 5 is useless and the alliance weak.
Edited by: M. Sass
