Limited unity: the loopholes in NATO’s mutual defense vows

The outcome of the upcoming presidential election is going to have major consequences for the relationship between the United States and its allies.

While President Joe Biden is a firm believer in the value of the transatlantic alliance, Republican contender Donald Trump has for years railed against US participation in the North Atlantic Treaty Organization (NATO).

In February 2024, for example, Trump said that if he were reelected president, he would tell Russia to do “whatever the hell they want” against NATO members who are “delinquent” in not having invested enough in their own military capabilities. Foreign policy commentators viewed that as an invitation for Russia to attack these NATO countries.

In September 2022, six months after Russia’s full-scale invasion, Ukraine applied to join NATO. Now, Ukraine’s potential membership is one of the top questions that representatives from NATO’s 32 member countries in North America and Europe will consider when they meet in Washington in July.

At the root of debates over policy toward alliances such as NATO is the assumption that NATO requires its members to step in and help with defense if another member of the alliance is attacked.

As political scientists who study the role of international organizations like NATO, we think it is important to understand that, in reality, alliance agreements are more flexible than people think.

In practice, it is possible for the US and other Western countries to stay out of a conflict that involves a NATO country without having to break their alliance commitments. The NATO treaty’s language contains loopholes that let member countries remain out of other members’ wars in certain situations.

What does Article 5 really mean?

One key part of