Article 42.7: Are EU states compelled to collective defense?

US President Donald Trump's rhetoric on everything from punitive tariffs to "ownership" of Greenland has been prompting 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 Article 5 of the North Atlantic Treaty Organization (NATO), which pledges that an attack on one signatory state would be seen as an attack on all, if called upon.

But whether or not this collective defense clause holds, there is another, lesser known collective defense 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.

So, what does this mutual defense clause entail, and are EU members likely to follow through should the article be invoked?

What is the EU's Article 42.7 and how does it differ from NATO's Article 5?

In 2009, the European Union introduced a mutual defense clause under Article 42.7 of the Lisbon Treaty 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 further clarifies that this obligation "shall not prejudice the specific character of the security and defense policy of certain member states" — a recognition that countries whose main defense commitments are shaped by NATO. 

Juraj Majcin, security and defense policy analyst at the Brussels-based European Policy Center, told DW that the main difference between the EU and NATO mutual defense clauses lay in the way defense support was to be delivered. While the EU provision was largely based on intergovernmental and bilateral assistance, the NATO's collective defense clause reflected a broader, more structural deterrence principle.

Former German MP for the Social Democrats and defense policy specialist Kristian Klinck believes the EU's Article 42.7 is more compelling than NATO's Article 5 — at least on paper. The requirement to provide help "by all means in their power," was widely interpreted to mean "to the end of one's strength," he told DW.

In contrast, Article 5's wording gives NATO nations more national discretion, allowing each country to take "such action as it deems necessary, including the use of armed force."

Nevertheless, both experts underlined that assistance under Article 42.7 did not just mean military support, but could also take the form of diplomacy, humanitarian aid and financial backing. This could be particularly relevant to non-aligned EU members Austria, Cyprus,  Ireland and Malta who traditionally avoid formal military alliances.

Has either defense clause ever been tested?

NATO's Article 5 has been activated only once in its history, after the 9/11 attacks in the US in 2001. In response, 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.

Similarly, the EU's Article 42.7 has also only been invoked once — also in response to terrorism. In 2015, following ISIS-led attacks in Paris, Germany and other EU members supported French forces with naval and air assets, but this was mostly as part of a US-led anti-ISIS coalition. 

Security analyst Majcin cautioned, however, that in both instances, the collective defense clauses had been applied in response to events "they were not designed for." Klinck agreed, arguing that France "faced a terrorist attack in 2015, but not a major military attack," 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 been busy boosting NATO defense spending and integrating their military systems. Klinck believes Europe still has a long road ahead to building up defense capabilites, but points out that progress has been made. 

"The Dutch land forces are fully integrated with German land forces. They operate and train together," Klinck explained. He also pointed to Dutch and Belgian naval cooperation. "If we can keep up this work and act in the spirit shown by European leaders in Davos when they reacted to Trump's comments on Greenland we are up to the task," he added.

NATO chief Mark Rutte recently 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 agrees. "When we talk about Europe's capacity to defend itself without the United States, we should not think only about a large-scale attack like in Ukraine," he told DW. "Russia wants to destroy NATO politically, to show that Article 5 is useless and the alliance is weak."

Edited by: M. Sass