Imagine for a moment that Poland annexes Ukraine. For simplicity let's assume that:

  1. Poland annexes only those parts of Ukraine which are not under the control of Russia or Russian proxies (i.e. Crimea and Luhansk/Donetsk republics are not annexed), and it does not stake any claims to those territories.
  2. The annexation takes place after a referendum in Ukraine took place, in which 60% of population voted for being annexed by Poland, and which was recognised by international community as free and fair.

Question: would this new Poland still be a NATO member after the annexation?

(I know this is not even a remotely realistic situation; I bet Ukrainians would vote against any annexation in the traditional sense of the word, i.e. being completely governed from Warsaw. More realistic would be a formation of a new state similar to UK which contains Poland and Ukraine as countries, but in this case I think I know the answer, so I want to strictly stick to this unrealistic scenario.)

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    Why would the membership be revoked?
    – phoog
    Commented Feb 2, 2022 at 23:16
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    @phoog Well, imagine for example the following scenario: Lithuania "annexes" Kaliningrad enclave, then Russia attacks Lithuania in response, then Lithuania invokes NATO article 5. Very likely this invocation would be considered by other members "not in the spirit" of the purpose of NATO, wouldn't it? So it's not unreasonable to enquire whether there is a built in mechanism in the NATO treaties against this kind of situations. Commented Feb 2, 2022 at 23:24
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    @Stuart F I thought that there might be some other treaties apart from the foundational ones which specify additional rules, requirements etc. Commented Feb 3, 2022 at 14:50
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    You are engaging in a bit of equivocation as to whether you're talking about a hostile annexation or a consensual one. In the question you go out of your way to say it's consensual, but then when asked in the comments why you think it would be a problem, you present a hostile one. Clearly Article V applies only to unprovoked attacks. If NATO had existed prior to WWII, Germany would not have been able to invoke Article V in response to the UK bombing them, because Germany initiated aggression. Commented Feb 3, 2022 at 20:00
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    @Erwan Your comment seems to be contradicitcting the established usages of the word annexation, e.g. here en.wikipedia.org/wiki/Texas_annexation Commented Feb 4, 2022 at 9:20

5 Answers 5


NATO member West Germany did annex East Germany, and remained NATO member. There were intensive consultations with other NATO members in the lead up to the annexation.

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    Technically, the FRG didn't annex the GDR, and doing so involved a contract co-signed by three major NATO powers. So it is a bad example.
    – o.m.
    Commented Feb 3, 2022 at 5:11
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    According to wikipedia, "The post-1990 united Germany is not a successor state, but an enlarged continuation of the former West Germany.", so certainly this is applicable in the context of my question Commented Feb 3, 2022 at 9:58
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    @ŁukaszGrabowski that's true, but according to the actual treaty I'm not sure that interpretation holds up... it refers to a new united Germany consisting of the territory of the Federal Republic and the GDR and the whole of Berlin.
    – CDJB
    Commented Feb 3, 2022 at 10:45
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    @CDJB German wikipedia discusses explicitly the two options which were on the table ("Beitritt der DDR zur Bundesrepublik.." and "Fusion von DDR und ...") and explicitly states that "Beitritt" option was chosen, so I think at least from the point of view of West Germany (i.e. of pre-1990 Bundesrepublik Deutschland) what happened was exactly the same as if say Jamaica was admitted to the US as a 51st state. But I see that indeed this is not directly addressed in the actual treaty you linked (perhaps the treaty happened first, and only afterwards technical choices were made) Commented Feb 3, 2022 at 13:33
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    @Erwan The situation that actually happened with the two Germany's matches the hypothetical situation in the question. Also, the wikipedia article you link lists non-forceful examples, such as the annexation of the Republic of Texas by the USA (the violent part was the prior separation of Texas from Mexico).
    – Arno
    Commented Feb 4, 2022 at 17:21

Possibly. The text of the actual NATO treaty is quite short and accessible. There is no article requiring the removal of a state that annexes or invades a neighbor. In fact, there's no expulsion language at all. But the general understanding when enacted was the lack of an expulsion clause wasn't an issue, as any state that failed to live up to the ideals set up in Article 1 and 2 could be declared in material breach of their treaty obligations:

Article 1 The Parties undertake, as set forth in the Charter of the United Nations, to settle any international dispute in which they may be involved by peaceful means in such a manner that international peace and security and justice are not endangered, and to refrain in their international relations from the threat or use of force in any manner inconsistent with the purposes of the United Nations.

Article 2 The Parties will contribute toward the further development of peaceful and friendly international relations by strengthening their free institutions, by bringing about a better understanding of the principles upon which these institutions are founded, and by promoting conditions of stability and well-being. They will seek to eliminate conflict in their international economic policies and will encourage economic collaboration between any or all of them.

After the dissolution of the USSR, NATO also set out a "Membership Action Plan" that prospective members would have to meet in order for their application to NATO to be approved. The five major requirements are:

--New members must uphold democracy, including tolerating diversity.

--New members must be making progress toward a market economy.

--Their military forces must be under firm civilian control.

--They must be good neighbors and respect sovereignty outside their borders.

--They must be working toward compatibility with NATO forces.

Technically speaking, these are only requirements for entering NATO, not ongoing membership, and they were only laid out after Poland had already joined. But in combination, there is a strong assumption that NATO members act and look a certain way. Even if Poland's annexation was bloodless and done in a bare democratic fashion, it would pretty clearly be in violation of NATO's general request that members act like good neighbors and promote regional stability.

The question would then become whether other NATO members actually feel obliged to press the issue or look the other way (as they currently do for a lot of Turkey's bad behavior). Unlike the democratic ideals promoted by NATO, the "good neighbors" expectation is also one of practicality. NATO is obligated to come to the defense of Poland if they are attacked, the expectation from other NATO states is that Poland in return should not be out there provoking conflict with its neighbors and forcing them into unnecessary and unjust wars.

The thing to keep in mind here is treaties are only as strong as the will to abide by them. The text of the NATO obligations could be clear cut in Poland's favor, but if the other NATO states don't want to come to Poland's aid, the international treaty police are not going to show up and make them. If Poland says "We're in NATO," and every other participating nation says "ah, but we'd prefer if you weren't," practically speaking, Poland is not in NATO any longer and the question if they legally are is entirely academic.

  • To avoid misunderstanding, could you say explicitly why in the situation I described "it would pretty clearly be in violation of NATO's general request that members act like good neighbors and promote regional stability." ? Commented Feb 3, 2022 at 17:50
  • From the perspective of Russia, it would effectively be the same as Ukraine joining NATO. Right now Ukraine and Belarus are buffers between NATO and Russia, the annexation would reduce that buffer to a mere roadbump. Commented Feb 3, 2022 at 20:25
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    Tangential comment: it's an interesting point of view. I tend to think that creating a Poland-Ukraine state would be economically extremely beneficial to both nations, if there ever was will on both sides (which there isn't). And this opinion of mine is based purely on considerations of economy, not military alliances. But it seems that you're (not unreasonably) suggesting that even if there was an overwhelming will to form Poland-Ukraine state, both nations would essentially have to first ask Russia for permission. Commented Feb 3, 2022 at 23:05

The answer is no. Turkey has annexed the north part of Cyprus even without any kind of referendum and is still a NATO member.

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    I don't think Turkey has annexed any part of Cyprus? Commented Feb 2, 2022 at 21:25
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    @ŁukaszGrabowski Oh, if you leave it as one or both of two present NATO members did bad things in Cyprus and are still members it answers the question plenty well. This situation is just not what NATO's scope of concern is - resisting external invasion - , directly. Commented Feb 2, 2022 at 23:51

This would be an unprecedented situation, and taking analogies from history are pointless. NATO members have committed to consult on security questions and to plan together.

  • Either the annexing member has consulted and has the consent of the other members. Then it should be equally easy to extend membership to the rump state that is to be protected.

  • Or the annexing member has not consulted, then that will earn the wrath of the other members. Possibly up to the point where the political guarantees of NATO protection are no longer credible.

  • The only scenario where this could be remotely relevant is if a cabal of powerful NATO members wants to sidestep the formal NATO processes, but then they could always unilaterally give guarantees with the same scope as Article 5.

  • Perhaps it is not clear to you but the intent of the question was to specifically determine if there's a mechanism built into any NATO treaties designed specifically to deal with annexation. The statements which you are making, namely that in absence of such a mechanism it would be a question of negotiations between NATO members, is clear. But again, the question was about presence/absence of such a mechanism Commented Feb 3, 2022 at 10:02
  • Isn't annexing without consulting the annexed territory against international law?
    – doneal24
    Commented Feb 3, 2022 at 16:36
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    @doneal24, the OP assumed just such a consultation for purposes of this question.
    – o.m.
    Commented Feb 3, 2022 at 16:39
  • @ŁukaszGrabowski, my answer is that assuming that there must be such a mechanism is a misunderstanding of NATO. NATO was always the bet that the US would sacrifice New York to avenge Paris, because they could either fight together with western Europe or a couple of years later alone, without them. Europe never quite believed that, hence the UK and French independent nuclear deterrence. The UK hedged against the US nerve failing when push came to shove by buying American missiles, France hedged against the US splitting from Europe by building a tout azimut nuclear deterrent.
    – o.m.
    Commented Feb 3, 2022 at 16:45
  • I don't think anyone, certainly not me, is "assuming that there must be such a mechanism", essentially my question is whether there is such a mechanism explicitly specified on the level of signed treaties. Commented Feb 3, 2022 at 17:22

There are the rules and there is reality. There are multiple examples of annexation of territories not leading to problems with NATO. For instance, Turkey has de-facto annexed the north-western part of Syria. Whether it eventually does it formally or not doesn't matter as far as Turkey's NATO membership. Considering that purchasing Russia's S-400 system despite the threat of US sanctions hasn't even raised the question of Turkey's NATO membership, we can see that the bar for expulsion from NATO is extremely high, indeed.

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