Why would Ukraine joining NATO at the present time not result in an immediate state of war between NATO members and Russia because of Article 5 obligations to defend a member state under attack? I always assumed that peace between Russia and Ukraine was an implicit precondition of Ukrainian membership for this reason. Yet proponents and opponents of NATO membership for Ukraine don’t seem to assume it would necessarily bring the US and most of Europe into the war right away. What understanding of Article 5 leads to this assumption?

Or is there a provision to prevent this scenario? I’m thinking specifically in terms of the treaty obligations, not other geopolitical considerations.

What inspired the question: this editorial https://www.wsj.com/articles/ukrainians-die-as-america-dawdles-russia-putin-nato-kgb-war-aid-weapons-europe-membership-b76f010 where Garry Kasparov advocates that Ukraine should be a NATO member. There is no mention of Article 5 being triggered or not. Any counter views like “this is unwise because it would provoke Russia” also seem to imply that Article 5 doesn’t simply decide the issue in favor of war.

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    "Yet everyone is talking about NATO membership for Ukraine" Are they?
    – James K
    Jul 9, 2023 at 19:23
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    We can't predict what would happen in the event that Ukraine joins NATO as if the join the terms could easily include that it would not result in article 5 or they could easily include that it will result in article 5 or they could say nothing about it There is too much unknown about what is happening behind the scenes to speculate on it.
    – Joe W
    Jul 9, 2023 at 19:32
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    Specifically, I’m thinking of Kasparov’s call for NATO membership for Ukraine in the Wall Street Journal and Biden’s current position against it. Proponents of either position seems to agree that NATO membership for Ukraine bears some risk of “escalation” but would not directly commit NATO states to go to war with Russia immediately. This implies that my prior understanding of NATO treaty obligations (specifically the part where an attack on one is considered an attack on all) is wrong. But I still don’t understand why. Jul 9, 2023 at 19:35
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    I think the implication is that Article 5 relates to attacks on states that are already members of NATO. The Article is meant to deter anyone (or honestly, you know, Russia) from attacking a member state. If a state is already at war when it joins NATO, the purpose of membership as a deterrent doesn't apply, and so Article 5 isn't technically meaningful. All it would really do is commit NATO to supporting Ukraine in their pre-existing war, which they are already doing. The difficulty is that Russia might not see it that way, which could lead to unwanted escalations from their side. Jul 9, 2023 at 19:50
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    @sfxedit Nato terms don't cover this situation unless you're just going to cite Article 5, in which case this is too trivial a question to ask. Article 5 has only been invoked once, in completely different circumstances, it's not clear on what basis Ukraine would join Nato, and there's no way to answer this without a vast amount of speculation.
    – Stuart F
    Jul 10, 2023 at 9:02

3 Answers 3


NATO membership for Ukraine would not directly lead to the other NATO members being at war with Russia. But they would have promised to restore the security of Ukraine.

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 [...] such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.

In theory, NATO could admit Ukraine and not "deem it necessary" to defend the entire territory of Ukraine with armed force. In practice, that seems unlikely unless the accession agreement clearly specifies which parts of Ukraine are NATO territory and which are not. (Remember the Falklands? British, but not NATO.)

The US President, among others, made it clear that in the present day, Article 5 means they will defend "every inch" of NATO territory. That's a political red line, while the text of the article says slightly less.

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    If the current support for Ukraine already would satisfy Article 5, that partly resolves my confusion. Jul 9, 2023 at 20:02
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    @WilliamDewey, NATO said they would defend, say, Latvia, with much greater force than they support Ukraine right now. They don't want to put question marks over the level of support for current members.
    – o.m.
    Jul 10, 2023 at 4:13
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    With regards to the Falklands, it's worth noting that they are not "in Europe or North America" or North of the Tropic of Cancer, so not covered by Article V anyway. Interestingly, I suppose this would also technically mean that Guam, Saipan, and even the main islands of the U.S. state of Hawaii are not covered, as they are not in North America and are South of the Tropic of Cancer. But, amusingly, French Frigate Shoals and Midway Atoll would be covered, as they are North of the Tropic of Cancer. So, Russia can invade Honolulu without triggering Article V, but not Midway.
    – reirab
    Jul 10, 2023 at 15:27
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    @reirab while the territories you cite may be north of the Tropic of Cancer, they are not covered by the treaty. The full phrase is "the North Atlantic area north of the Tropic of Cancer," and these territories are not in the Atlantic.
    – phoog
    Jul 12, 2023 at 11:29
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    @phoog, see the Turkey clarification in Article 6 for how this would work. The NATO members are free to define the threaty area to include non-Atlantic territories if they like.
    – o.m.
    Jul 12, 2023 at 15:13

tl;dr: Gray area

Article 5 states:

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 Article 6 clarifies an armed attack:

on the forces, vessels, or aircraft of any of the Parties

Neither article specifies what exactly an "armed attack" is, nor whether each individual strike, offensive or even bullet fired would constitute one or if it would consider the entire operation one "armed attack". It also does not have anything to say about an ongoing conflict at the time of joining. If you wanted to, however, you could say that any shot fired at any soldier, tank, etc. of Ukraine after the moment of joining constitutes an armed attack and triggers Article 5.

As for the joining itself, there is no checklist of NATO membership.

All this leaves considerable gray areas. From new reports and interviews such as this one, we can see that at least a number of important people do believe that if Ukraine were to join at this time, Article 5 would be triggered.

  • Article 6 limits Article 5 to specific areas and forces, vessels or aircraft in or over these areas. in 1951 is was changed to include the Asian part of Turkey so it could be changed to not include parts of Ukraine (although that would defeat the purpose of NATO)
    – xyldke
    Jul 11, 2023 at 12:27
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    @xyldke could be changed, yes. But as it is written right now, if Ukraine were to join NATO than attacks on Ukraine forces, vessels or aircraft would trigger Article 5. But, of course, politicians being who they are, if they really wanted they would find a way to argue that the actual attack began in 2022, before Ukraine joined. It would be a contrived argument, but it could be made.
    – Tom
    Jul 11, 2023 at 13:01

It would not result NATO going into the Russia after Moscow, but I do not see how NATO makes any sense if they would not come to Ukraine, with they troops and all modern weapons.

The red line would be "we do not attack the internationally recognized (not Crimea, etc) territory of Russia directly". Of course, Russia has declared this line to be elsewhere, including statements that NATO is already at war with them and others that its territory now expands over annexed territories of Ukraine, mostly not recognized worldwide. NATO will need to risk ignoring this.

  • Also, they don't agree on what territories are and aren't part of Russia.
    – gerrit
    Jul 10, 2023 at 9:28
  • NATO will obviously take the own view into consideration: all former territory of Ukraine.
    – Stančikas
    Jul 10, 2023 at 11:54
  • Indeed. But I can see how NATO attacking military targets in Crimea would risk World War III, and probably senior politicians and generals see that as well.
    – gerrit
    Jul 10, 2023 at 11:56
  • This is likely the reason why they are not accepting Ukraine into NATO so far right now, on that we seem in consensus.
    – Stančikas
    Jul 10, 2023 at 12:02
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    @gerrit perhaps this is just me being pedantic but for it to be a World War, doesn't that mean Russia needs allies who are actually fighting? I guess Belarus is their ally but I don't think India or China is going to commit troops to fight with them. Jul 10, 2023 at 21:27

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