Would NATO Art. 5 be Invoked by Security Guarantees to Ukraine and, if so, Would a Member State be Excused from its Mutual Defense Obligation for Allies that Don't Meet their 2% GDP Investment Target?
In reaction to widespread calls to provide security guarantees to Ukraine,[1] several politicians have raised concerns about the potential for global conflict arising from NATO defense alliances. French RN leader, Marine Le Pen, for example, has stated that “Ukraine cannot win this war without the involvement of NATO, which is not an option given the risk of escalation towards a world war between nuclear powers.”[2] American President, Donald Trump, has similarly warned Volodymyr Zelensky that he is “gambling with World War Three” by requesting greater support from NATO allies.[3]
Secondarily, Trump has also said that in the event a NATO ally who does not meet their 2% GDP spending target is indeed attacked by Russia, triggering the US’s mutual defense obligation under the NATO treaty, he would not come to that member state’s defense at all.[4]
Are Le Pen and Trump correct that NATO support to Ukraine through of security guarantees bears the potential for world war, set in action by member states’ collective defense obligations? And, if so, would the US be excused from its mutual defense obligation under international treaty law for alliance members that fail to spend 2% of their GDP on national defense annually, per the NATO investment guideline?[5] The short answer to both of these questions is not really.
The NATO Treaty text discusses the collective defense obligation in its infamous Article 5, reading:
“The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.
Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security.”
This article is complemented by Article 6,[6] which stipulates:
“For the purpose of Article 5, an armed attack on one or more of the Parties is deemed to include an armed attack:
● on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France 2, on the territory of Turkey or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer;
● on the forces, vessels, or aircraft of any of the Parties, when in or over these territories or any other area in Europe in which occupation forces of any of the Parties were stationed on the date when the Treaty entered into force or the Mediterranean Sea or the North Atlantic area north of the Tropic of Cancer.”
As plainly stated in the text of Article 5, the NATO collective defense obligation only arises when a member state would be able to individually exercise its right of self-defense. Therefore, a member state acting in a strictly offensive capacity, such as the United Kingdom if they sent “boots on the ground and planes in the air”[7] to Ukraine, would not be considered “under attack” within the terms of the treaty, should those troops be targeted by Russian missiles on Ukrainian soil. Article 5 would only be invoked in the very unlikely event Russia strikes UK forces or civilians on UK soil or strikes a UK military base in Europe which was already there prior to the conflict. In fact, the strict geographical limits of the treaty were specifically lobbied for by the US in order to exclude the many colonial territories under control of European member states at the time of the signing.[8]
Nonetheless, even if Article 5 were invoked, the assistance provided by other Allies does not “necessarily [have to be] military and depends on the material resources of each country.”[9] This is reflected in Article 5’s phrasing that Allied Members are only required to “assist the Party […] attacked by taking […] action as it deems necessary.”[10]
Finally, it is widely accepted that a NATO member’s failure to meet the 2% GDP spending guideline would not automatically provide a right to renounce the mutual defense obligation, because it would not constitute a “material breach” under international treaty law.[11] It is also important to stress that the 2% figure, established in 2006 is a mere guideline which primarily “serves as an indicator of a country's political will to contribute to NATO's common defen[s]e efforts.”[12]
Kenza Tahri is a staff member of Fordham International Law Journal Volume XLVIII.
[1] See, e.g., Kier Starmer, Prime Minister, Oral statement to Parliament: PM statement to the House of Commons (U.K. ) (March 3, 2025) https://www.gov.uk/government/speeches/pm-statement-to-the-house-of-commons-3-march-2025. Starmer has set out to ally a ‘“coalition of the willing’ ready to defend a deal in Ukraine and guarantee the peace. […] with, if necessary […] boots on the ground and planes in the air.”; see also Léonie Chao-Fong et al., Macron open to extending France’s nuclear umbrella to European allies, The Guardian (Mar. 5, 2025, 5:00 PM), https://www.theguardian.com/world/live/2025/mar/05/donald-trump-volodymyr-zelenksyy-ukraine-russia-greenland-tariffs-europe-live-news (Macron saying “European military forces could be sent to Ukraine if a peace deal is signed”).
[2] Marine Le Pen, Party Leader, Rassemblement National, Discours de Marine Le Pen sur la situation en Ukraine, Youtube (Mar. 3, 2025), https://www.youtube.com/live/3mp6ROB56rg?si=B_ksoTQn375dMGmn.
[3] Tom McArthur & Jaroslav Lukiv, Trump accuses Zelensky of 'gambling with World War Three’, BBC (Feb. 28, 2025), https://www.bbc.com/news/articles/c9dejydynngo.
[4] Kate Sullivan, Trump says he would encourage Russia to ‘do whatever the hell they want’ to any NATO country that doesn’t pay enough, CNN (Feb. 11, 2024), https://www.cnn.com/2024/02/10/politics/trump-russia-nato/index.html. The journalist reports that ‘“Trump said ‘one of the presidents of a big country’ at one point asked him whether the US would still defend the country if they were invaded by Russia even if they ‘don’t pay.’
‘No, I would not protect you,’ Trump recalled telling that president. ‘In fact, I would encourage them to do whatever the hell they want. You got to pay. You got to pay your bills.’”
[5] North Atlantic Treaty art. 5, Apr. 4, 1949, 63 Stat. 2241, 34 U.N.T.S. 243.
[6] North Atlantic Treaty art. 6, Apr. 4, 1949, 63 Stat. 2241, 34 U.N.T.S. 243.
[7] See Starmer, supra note 1.
[8] See Broderick C. Grady, Article 5 Of The North Atlantic Treaty: Past, Present, And Uncertain Future, 31 GA. J. Int'l & Comp. L. 167, 181. “[T]hough the United States eventually saw the wisdom in allying itself with the Western European nations, it recognized the potential for disaster if Article 5 could be invoked as a result of an attack on the many colonial territories then held by the European Member States throughout the world. As a result of American influence, strict geographical limits were placed on Article 5; the final version of Article 6 excluded virtually all European colonial territory except the Algerian departments, and then only after considerable pressure from France.”
[9] See Collective defence and Article 5, NATO (Last updated: Jul. 4, 2023, 11:47), https://www.nato.int/cps/bu/natohq/topics110496.htm.
[10] See North Atlantic Treaty, supra note 5.
[11] See Richard Pado, Paying Their Fair Share: The Relationship Between Funding And Mutual Defense Obligations In Nato, 47 Syracuse J. Int'l L. & Com. 343, 355–56.
[12] See id.
This is a student blog post and in no way represents the views of the Fordham International Law Journal.