What if NATO members go to war against each other?

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In the summer of 2020 the tensions between NATO allies Turkey and Greece were once again rising, reaching alarming levels. The conflict between the two countries was about who owned the rights of key parts of newly discovered gas fields in the Eastern Mediterranean.1 The world was carefully watching, as both countries were having a war of words. Amid the altercation, both countries were preparing for possible military actions. Luckily, this conflict deescalated just in time and a possible war between Turkey and Greece was avoided.

However, this conflict has raised several controversial questions: what if this altercation between two NATO allies did escalate, leading to the beginning of a new armed war? Considering there are no such precedents, what would this mean for the fighting allies and in what way will NATO interfere?

“The most important players of the NATO are the member countries themselves.”

NATO: what is it?
North Atlantic Treaty Organization (for short NATO) is an intergovernmental military organization consisting of 30 European and North American countries. The main goal of NATO is to implement the North Atlantic Treaty (NAT) which purpose is peacekeeping and forming a collective defence against any attacks from threatening parties. The Treaty consists of 14 articles summing up the duties of the members, guidelines and further actions that can be taken when the Treaty is instated.2

“The Treaty doesn’t dedicate any explicit provisions regarding members attacking each other.”

The NATO Treaty is up for interpretation
The goal of collective defence is codified in Article 5 NAT. It states that an attack against one member of NATO should be considered an attack against all. In this case, all other NATO allies will assist the said attacked member. However, the article doesn’t mention anything specific about a member attacking another member.3 In fact, the Treaty doesn’t dedicate any explicit provisions regarding members attacking each other. Also, it is important to note that this article does not make a distinction between NATO members and external attacking parties. This could imply that the article could even be triggered when the attacking party is a NATO ally. Since an event like this never occurred, there are no precedents to look into.

Another Treaty article that could give us more insights into the consequences of such conflict between allies, is Article 8 NAT. The specific article states that ‘Each Party undertakes not to enter into any international engagement in conflict with this Treaty’.4 Knowing that the main purpose of the Treaty is peacekeeping and preventing attacks against NATO members, this could imply that fighting allied nations means disobeying the article and therefore breaching the Treaty.

What would it mean for the fighting NATO members?
Since the Treaty itself doesn’t have explicit provisions on governing a war between NATO allies, the consequences for such actions are not perfectly clear. However, the Treaty gives guidelines which could provide a potential, yet discussable answer.

Article 5: The possibility of attacking another ally
If a member of NATO is attacked by another member it would, in theory, mean Article 5 NAT will take effect: an attack against one member is an attack against all NATO members. According to this article, the attacking ally will be targeted. The said member could be seen as the initiator or so-called ‘aggressor’. The consequences for the ally could depend on whether they are the aggressor or not. However, in reality, determining an aggressor in a complex military conflict could not always be that easy if both parties are fighting. Even if this would be possible, the Article on its own is rather confusing and up for interpretation in this scenario. This would mean both countries would trigger this clause.

“Assuming that both countries are breaching the Treaty it is still unclear what the consequences would be.”

Article 8: The possibility of expelling allies from NATO?
Article 8 NAT could give more clarification on what the consequences could be for members that get into a military conflict with each other. The Article summons an obligation to refrain from any activities that could form a conflict with the provisions mentioned in the Treaty. Whenever an allied member decides to attack another ally it would mean that they breach Article 8 (and with it the fundamental principles) of the Treaty.

The consequences could depend on what role the fighting country would have. For example, if a country that is attacked is purely fighting back out of self-defence, the collective self-defence, as mentioned in Article 5 NAT, may be in favor of the defending country.5 Assuming that both countries are breaching the Treaty (Article 8 and Article 5 NAT) it is still unclear what the consequences would be. The Treaty itself doesn’t have any provisions dedicated to expelling any members.6

What would NATO (members) do?
As mentioned before, NATO has the main goal of keeping the peace, deescalate and – if necessary – help out the attacked member. However, when the conflict is between two NATO members it gets complicated. For example, with the quarrel between Turkey and Greece, allied countries can even take sides, like France backing up Greece.7 A war scenario can raise question whether NATO members will also take sides. Since NATO is an intergovernmental organization the sovereignty lays by members, which gives them the choice in what way they want to help an attacked member based on the Article 5 NAT.

A question that is still up for debate
The latest tensions between Greece and Turkey have raised a significant problem within NATO: the lack of procedure and action in the possible scenario of its members attacking each other. Furthermore, because of this conflict, it has been pointed out the lack of specificity within the Treaty. Therefore, in the case of a military conflict between two NATO allies, there seem to be two disputable actions that NATO can take: the possibility of attacking the “aggressor” country and the possibility of expelling the allies that have breached the Treaty. However, these two actions are still up for debate and there is still no clear procedure for such events, which raises questions about the agreements and security provided by NATO.

Soner Korucu


1. BBC, Turkey-Greece tensions escalate over Turkish Med drilling plans, 25 August 2020, found on: https://www.bbc.com/news/world-europe-53497741.

2. NATO, What is NATO?, found on: https://www.nato.int/nato-welcome/index.html.

3. NATO, Collective Defense – Article 5, 25th of November 2019, found on: https://www.nato.int/cps/en/natohq/topics_110496.htm.

4. NATO, The North Atlantic Treaty, 10th of April 2019, found on: https://www.nato.int/cps/en/natolive/official_texts_17120.htm.

5. C.G. Cooper, NATO Rules of Engagement, Leiden: Brill/Nijhoff 2019, p. 244.

6. EenVandaag, B. Boxhoorn, Kan je een land uit de NAVO zetten?, 11th of November 2020, listen on: https://www.nporadio1.nl/radio-eenvandaag/onderwerpen/67743-2020-11-11-kan-je-een-land-uit-de-navo-zetten.

7. The Guardian, France to send warships to support Greece in Turkey standoff, 29th of January 2020, on: https://www.theguardian.com/world/2020/jan/29/greece-turkey-standoff-france-send-warships-east-mediterranean.


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