Given that the common security and defense policy "also entails collective self-defence amongst member states" with the only (and debated) exceptions being Austria, Ireland, Finland, Malta and Sweden (having been previously declared neutral countries). How can Ukraine join the EU without forcing the entire EU into war with Russia? Since a vast majority of EU members are also NATO members, would this also force NATO into the conflict?

I realize there's a practical, political aspect to this, but strictly from a legal perspective, are these treaties binding? If not, why not?

  • Dis you read the citation '[a]', that comes directly after your qouted portion? In most treaties, such events are only binding when the event occurs after the treaty comes into effect (not before or durring). I believe that is the case with NATO. Jun 22, 2022 at 20:02
  • @MarkJohnson I did read the citation, I don't see any reference to the timeline being relevant. The only quote is "If a Member State is the victim of armed aggression on its territory, the other Member States shall have towards it an obligation of aid and assistance by all the means in their power, in accordance with Article 51 of the United Nations Charter. This shall not prejudice the specific character of the security and defence policy of certain Member States." Even if that's the case, would Russia instantly leave Ukraine to avoid a conflict with the entire EU if the treaty is signed?
    – TCooper
    Jun 22, 2022 at 20:07
  • Only time will tell for those who don't have a functual crystal ball... Jun 22, 2022 at 21:22
  • @MarkJohnson Fair, I'm just looking for letter of the law though - this could be a fun question for politics too. Either way the war should be over well before Ukraine can move from candidacy to ascension / actually join. Average time is almost 5 years, similar countries (not in the middle of a war) all took longer than average - purely a curiosity
    – TCooper
    Jun 22, 2022 at 22:00

2 Answers 2


Yes, for most of them.

Article 42.7 TEU
If a Member State is the victim of armed aggression on its territory, the other Member States shall have towards it an obligation of aid and assistance by all the means in their power, in accordance with Article 51 of the United Nations Charter. This shall not prejudice the specific character of the security and defence policy of certain Member States.
Commitments and cooperation in this area shall be consistent with commitments under the North Atlantic Treaty Organisation, which, for those States which are members of it, remains the foundation of their collective defence and the forum for its implementation.

The "specific character" for "certain Member States" refers to states with a traditional military neutrality, notably Austria, Ireland, and Sweden. Those EU states which are also NATO members would not have that excuse since they agreed, in principle, to use military force to protect others, so they cannot say they are constitutionally incapable of doing so in the EU case.

This is why the EU does not, generally, admit members with open territorial conflicts.

Probably no, for the rest of NATO

Article 5
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 recognised 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.

This is in a way weaker than the EU clause, "such action as it deems necessary" might allow individual countries to do less than going to war if that is unnecessary. Also, NATO-but-not-EU countries might claim that a Russian attack on EU forces in an EU-but-not-NATO country does not constitute an attack in the treaty area:

Article 6
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, [...]

How to interpret a Russian counter-counter-attack on NATO countries after those counter-attack Russia in accordance with collective defense after a Russian attack on a non-NATO country would become a political issue.

As pointed out in the comments, the practical application of either TEU 42.7 or NATO Article 5 would be intensely political, not just in the "indirect" case but also where it seems to be clear-cut. Nations might rally to the flag or drag their feet, depending on the details. Or even depending on totally unrelated issues where they want to get concessions. Or they might alert their forces and deploy them on different flanks than the one under attack, because that flank feels exposed.

  • Thanks, I think your answer lines up with how I've been reading the documents, but I'm certainly not an expert. I think @DaleM's answer covers the practical application of the law, while this covers the theoretical/letter of the law. Is that an accurate summation of the differences in the answers?
    – TCooper
    Jun 23, 2022 at 14:14
  • I made a comment about this on my answer, and while not strictly a legal response, it may be worth noting something about how this won't throw all of Europe into war if the EU votes to accept Ukraine's candidacy today. Given the long lead time from candidacy to membership there is a very low likelihood of the CSDP being relevant in the current conflict (hopefully it's resolved in far less than ~5 years anyway). Further it doesn't seem feasible to meet the EU's requirements while at war anyway. Maybe not worth adding, just worried about my question being seen as fearmongering or something.
    – TCooper
    Jun 23, 2022 at 14:20
  • Curiously, I’ve mostly heard people describe NATO’s guarantee as stronger than the EU’s. I assume much of that is the superpower backing it up, but I wonder if NATO being a military alliance at its core also plays a role in that perception.
    – cpast
    Jun 24, 2022 at 3:21
  • @cpast, also, NATO has joint infrastructure and regularly trains together. That gives a habit/assumption of cooperation.
    – o.m.
    Jun 24, 2022 at 4:29

Probably not

First, going to war is primarily a political, not a legal decision. Even if a treaty clearly requires a country to do something, they can always break the treaty and the consequences are usually political, not legal.

Second, this would be decided before the treaty was signed as part of the process of negotiating the treaty.

Third, and this is the legal out, Ukraine was not a “Member State” at the time of the aggression.

  • Thanks, while in practice I agree its political, isn't the definition of a treaty a legally binding agreement between two or more nation states? And of course you can break the treaty, but at that point aren't you violating international law? I know anyone can break the law without consequences if anyone else who could enforce it chooses not to, maybe I should rephrase the question to state "as currently written"? On the third point, would continued aggression in the same country still offer the out? i.e. the day after the agreement is in effect Russia bombards a new city with missiles
    – TCooper
    Jun 23, 2022 at 0:23
  • @TCooper Breaking a treaty does violate international law and normally wouldn’t be done lightly. That said, a decision to go to war isn’t taken lightly either.
    – cpast
    Jun 24, 2022 at 3:22

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