Limited Unity: The Loopholes In NATO's Mutual Defense Vows

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Why Gaza gets more attention than Xinjiang What does Article 5 really mean?

One key part of the NATO treaty that countries sign when they join the alliance is called Article 5 . This says that an“armed attack” against one NATO member in Europe or North America“shall be considered an attack against them all.”

In the case of such an attack, NATO countries agree to assist the country that requires help, including through“the use of armed force, to restore and maintain the security of the North Atlantic area.”

But the treaty does not include a clear definition of a what an“armed attack” actually is.

This mattered in February 2020, when Turkey asked for a NATO meeting and requested that NATO intervene with military force in response to Russian and Syrian forces' attacks on its territory, which had killed 33 Turkish soldiers, during the Syrian civil war.

NATO allies chose not to defend Turkey with military force, arguing that the level of violence against Turkey wasn't enough to call it an“armed attack.”

Other exceptions to the rule

Even when NATO members decide that Article 5 should apply to a specific situation, each country can still individually decide how to act. That is, while NATO does have administrative staff based in Brussels , there is no central NATO authority that tells each country what it must do.

An F-15 Eagle flies a combat air patrol mission over New York City on Nov. 6, 2001 Photo: US Air Force

Instead, each country tells NATO what it is – and is not – willing to do.

NATO members have only formally invoked Article 5 once – following the September 11, 2001, attacks on the World Trade Center and the Pentagon outside of Washington.

At that time, 13 NATO countries sent fighter aircraft to help the US patrol its skies from mid-October 2001 to mid-May 2002.

But most NATO allies chose not to send troops to Afghanistan to support the US in its fight against the Taliban. This lack of action on the part of some NATO allies was not seen as breaking the treaty and didn't prompt a major debate – and the countries that chose not to join the fight were not sanctioned by or ejected from the alliance.

The NATO treaty also provides some exceptions based on geography. When Argentina went to war with the United Kingdom (a NATO member) over the Falkland Islands in 1982, the US and other NATO members were able to use the fact that the alliance only applies to the North Atlantic region as a reason to stay out of the conflict.

Would public opinion force the president's hand?

Some political scientists argue that voters will demand their leaders take the country to war to defend an ally. This implies that what really binds the members of an alliance together is not the legal text of an international treaty itself, given that no international court is empowered to enforce the treaty , but rather the public's expectations of what it means to be an ally.

As part of our research into how the American public thinks about international legal obligations, we decided to construct an experiment to see if presidents could use alliance loophole language to justify keeping the US out of a war involving an ally.

In 2022 and 2023, we conducted a pair of survey-based experiments that involved asking nearly 5,000 American adults to consider a hypothetical scenario in which a US ally comes under attack from a powerful neighbor.

Some of the respondents were told that the text of the alliance treaty would allow the US government to avoid having to send troops to defend the embattled ally, while others were not told that information.