Many NATO member European countries govern territories far beyond their own borders, a legacy of the colonial era.

From the Caribbean to the Indian Ocean, parts of Europe lie thousands of kilometres from the continent, raising a fundamental yet unresolved question: does a collective mechanism exist for the defence of these regions?

According to an analysis published by Euractiv, in theory a NATO member can invoke Article 5 of the alliance’s treaty and request assistance if it comes under attack.

But the collective defence clause does not apply everywhere, and its geographic scope is actually defined in the far less well-known Article 6.

That article stipulates that for Article 5 to be triggered, an armed attack must occur “on the territory of any of the Parties in Europe or North America (…), on the territory of Türkiye or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer.”

NATO’s ultimate security guarantee therefore does not cover a large proportion of Europe’s overseas territories.

At this point, the question arises as to whether the EU’s mutual assistance clause can fill that gap.

Unlike NATO’s Article 5, Article 42(7) of the EU Treaties is not a mutual defence clause but a mutual assistance clause.

It does, however, contain no geographic limitation.

European External Action Service (EEAS) spokesperson Anitta Hipper confirmed to Euractiv that, if invoked, the clause provides a guarantee that “all EU member states are obliged to assist the member state that has suffered an armed attack on its territory ‘by all the means in their power’.”

EU mutual assistance is increasingly becoming a subject of political debate in Brussels.

Some member states remain cautious about its potential implications.

In particular, there is a risk that more explicit reliance on EU mutual defence mechanisms could accelerate a partial US withdrawal from the Continent.

EU diplomats are expected to conduct a simulation this week on the application of Article 42(7), which is politically defined but has never been clearly tested.

Colonial legacy: EU overseas territories

France is the EU member state with the largest number of overseas territories.

Paris controls French Guiana in South America, home to the ESA’s European Spaceport, as well as Guadeloupe, Martinique, Saint-Martin and Saint-Barthélemy in the Caribbean.

These territories lie below the Tropic of Cancer and are therefore outside the scope of NATO’s Article 5.

In the Indian Ocean, Réunion and Mayotte also remain part of the French state.

The security of these regions is the sole responsibility of the French armed forces, but as part of the European Union, any armed attack could prompt Paris to invoke the EU mutual assistance mechanism.

The Netherlands also possesses Caribbean territories, including Aruba, Curaçao, Sint Maarten, Bonaire, Sint Eustatius and Saba.

A spokesperson for the Dutch foreign ministry confirmed to Euractiv that because these territories are located south of the Tropic of Cancer, they fall “outside the geographic scope” of NATO’s Article 5.

“That said, a provision such as Article 5 is not necessary for allies to request or provide (military) assistance in the event of an armed attack on any of these territories,” the spokesperson added.

Unlike the situation with France, Aruba, Curaçao and Sint Maarten are autonomous countries within the Kingdom of the Netherlands.

Asked about Article 42(7), the ministry said the provision “speaks for itself” and “should be understood as an expression of solidarity among EU member states.”

According to Euractiv, the example of Greenland offers a useful comparison for better understanding the Dutch Caribbean.

Asked about the scope of EU assistance, the spokesperson confirmed that “Greenland is part of the territory of the Kingdom of Denmark and therefore falls within the scope of the mutual assistance clause.”

Moreover, because Greenland is located well north of the Tropic of Cancer, it is also eligible for NATO protection under the treaty’s geographic framework.

Spain presents another interesting case with regard to Article 6. Its North African exclaves of Ceuta and Melilla appear to occupy a grey zone, as they lie outside Europe and North America.

In 2022, ahead of the NATO summit in Madrid, the issue briefly surfaced in domestic political debate.

Spanish Prime Minister Pedro Sánchez appeared to dismiss the discussion.

Noting that Spain had been a NATO member for more than 40 years and that such doubts had never arisen, he said: “Ceuta and Melilla are Spain.”

While the applicability of NATO’s Article 5 may be debatable, no such ambiguity exists with respect to the EU’s mutual assistance clause.

Non-EU NATO overseas territories: Britain

As a NATO member outside the EU, the United Kingdom possesses 14 overseas territories under its sovereignty.

These territories are spread across the Caribbean, Atlantic and Pacific oceans, and most lie outside the core geographic scope of NATO’s Article 5.

Recent geopolitical debates, however, have put these regions back on the agenda, including heightened attention to the Falkland Islands dispute.

A recent internal email first reported by Reuters indicated that the US Department of Defense had considered revisiting Washington’s position on the sovereignty of the islands, partly because it viewed UK support as insufficient on the issue of a US-Israel war with Iran.

British overseas territories that fall outside the scope of NATO’s Article 5 rely entirely on London for their protection.

The US also faces a geographic issue. Hawaii lies south of the Tropic of Cancer.

Territories such as Puerto Rico, Guam, the US Virgin Islands and American Samoa also fall outside the treaty’s traditional North Atlantic framework.

They are therefore outside the strict geographic scope of Article 5, but can nonetheless rely on NATO’s largest military for their security.

This gap in the security architecture for overseas territories reflects the legacy of European states with global territorial footprints, even as collective defence systems rest on frameworks designed for a narrower Europe.

The result is that, in the event of a crisis, responsibility for overseas territories remains at times unclear.