Could NATO Accept a new member who is at war?

There are many reasons why NATO would not want to accept Ukraine as a new member state right now. The most prominent reason being the perception that this would increase the chance of a nuclear conflict. Now this may of course be true, but we may also be wrong here.

If, let's say, NATO were to consider accepting Ukraine, would it be possible at all? Are there limitations in the NATO charter that prohibit Ukraine from entering simply because they are presently in a state of war? Are there other major reasons why this is not an option?

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    I don't think there are formal treaty limitations but it would be rather unprecedented. One of the reasons for not admitting them before was the Donbas conflict politics.stackexchange.com/questions/71039/… And Russia almost certainly knew that. Commented Mar 29, 2022 at 12:35
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    We should not forget that NATO, and all international treaties, are just promises made of words and papers made by (mostly) selfish nations. Relying on it looks quite naïve. I'd be surprised if these alliances are respected, especially for countries with a high tolerance of falsehood and that have nothing to gain (we are rather unequal in cooperation and honesty). Let's not forget the Anglo-Polish alliance: en.wikipedia.org/wiki/Anglo-Polish_alliance
    – JinSnow
    Commented Mar 30, 2022 at 10:08
  • If you were living in some NATO countries (like the one I'm living in), you would have learned to distrust any official statements as concretely nothing even the laws and the constitution aren't really respected, and most of the time the self-interest goes above selfish interest of the nation. (Most?) people don't realize that very few NATOS members reach the state of the rule of law. My country isn't ruled by law, but arbitrary decisions. (We aren't living in anarchy, but simply in the old traditional natural model). The rule of law is a very recent and (I believe) a very rare system.
    – JinSnow
    Commented Mar 30, 2022 at 10:20
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    "Could X sign a paper that says Z?" can always be answered with a yes. Signing papers is easy. "Could X fulfill their promise to do Z?" is much more interesting. Commented Mar 30, 2022 at 19:07

3 Answers 3



NATO membership is by unanimous political agreement of the existing members. And only these members get to interpret the NATO rules. So, assuming political agreement, there will be nobody that will raise a legal objection.

Of course, when you change the question from "could they?" to "will they?", the rules become slightly more relevant. If we cannot assume political agreement, a country that disagrees with Ukraine's membership will likely prefer to formulate their objections in legalistic terms. Considering that NATO prefers to look united, such a political objection in legalistic terms will be probably accepted at face value by the other members. "My colleague from country X has brought up a good point. While the citizens of country Y would welcome Ukraine into NATO, we have to respect international treaty agreements. "

  • Basically you are saying that NATO members can bend their own rules. But what could be the political price paid to the bending of the rules?
    – FluidCode
    Commented Mar 30, 2022 at 10:39
  • @FluidCode If all agree none. If some disagree, well either no action or the split of the alliance. But if they agree that's basically a codified declaration of war as with the membership of the state in conflict the entire NATO would be part of that conflict. That's the situation from the POV of NATO. For the rest of the world that would basically send the signal that NATO could inject itself in any armed conflict if they want to. Though they could still do that anyway as Bush's wars have already set precedents. So politically it's mostly the question whether one wants to join the war or not.
    – haxor789
    Commented Mar 30, 2022 at 12:32
  • @haxor789 You are going in circles to avoid talking about the real problem. Of course prime ministers of weak states under US pressure would all agree to ignore those rules. But how can they face the people they were supposed to lead after that? How can they then explain to their people that notwithstanding the weakness in front of Russia they are still ready to drag them in a war?
    – FluidCode
    Commented Mar 30, 2022 at 19:24
  • @FluidCode I don't really get your question here. I mean either they have the mandate to make that decision in which case there's no immediate political backlash or they need to verify the mandate by idk having a referendum or at least have their local parliaments backup the mandate. And once the decision is ratified they basically have to role with that. Whether they win the next election with it is a different question, but that's hard to answer anyway.
    – haxor789
    Commented Mar 31, 2022 at 9:39
  • @FluidCode: Most of those "weak" NATO members have coalition governments. Putting their PM's under pressure would achieve little. They'd just point out that they don't have a personal mandate. Macron and Johnson are exceptions, but France and the UK are nuclear powers in their own right and permanent members of the Security Council. Not exactly "weak".
    – MSalters
    Commented Mar 31, 2022 at 13:38

YES, countries at war can still join.

Entry of new countries is controlled by Article 10 of the North Atlantic Treaty:

The Parties may, by unanimous agreement, invite any other European State in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area to accede to this Treaty. Any State so invited may become a Party to the Treaty by depositing its instrument of accession with the Government of the United States of America...

The most important limitation is that the current members of the alliance must unanimously agree to the new member. There's no restriction on whether new members are currently at war and a war that was legitimately considered to endanger "the security of the North Atlantic area" might be a perfectly valid reason to welcome the preferred side into the alliance. There are some minor restrictions: under the current treaty, new members have to be considered European; they should not have any existing obligations that might interfere with their NATO ones (Art. 8); and the US has to accept their formal paperwork. There's no legitimate reason the US would openly welcome a new member but then take issue with the formalities, but it is a potential avenue for some diplomatic kabuki. They could theoretically sign off on Ukraine joining at a NATO meeting but then refuse to accept their forms, for example, until after they had brought their military hardware in line with current NATO specs or some similar nonsense; such an excuse might be used to keep NATO forces from direct immediate conflict with Russia while laying a marker that Ukraine would join more fully at some date 5-10 years from now.

NO, Ukrainian membership would not automatically oblige the United States to go to war with Russia. NATO countries have worked together in several conflicts but the joint defense pact (Art. 5) has only been used once since NATO's founding: after 9/11 to bring the Europeans over into the Afghan fight, which would otherwise have been outside their purview. The treaty was very carefully worded to exclude an obligation to help with any colonial wars outside French Algeria (Art. 6) and, e.g., wouldn't've even been activated by a hot war during the Cuban Missile Crisis since it's south of the Tropic of Cancer. Assuming that Ukraine's territory is considered European, they would be able to invoke Article 5 protections but Sen. Vandenberg very carefully added in provisos that it was never a blanket protection in all cases. It allows that each NATO member "will assist... by taking forthwith, individually and in concert... such action as it deems necessary..." (Art. 5) "...in accordance with [its] constitutional processes" (Art. 11). Ukraine could join NATO and the other countries in it wouldn't be able to leave for a year (Art. 13) but the US president could restrict its aid to humanitarian work or the US Congress could overrule presidential moves to go to war by withholding authorization and necessary funding. That would not only fit within the NATO charter; the NATO charter was specifically designed to give the US that kind of leeway.

NO, they still shouldn't let such countries in. The NATO countries could go to war against Russia now if they really consider that essential for North Atlantic security; Ukraine doesn't need to be a member for them to protect their own interests. The whole point of NATO is to avoid wars, achieving peace through prohibitive strength that keeps anyone from launching direct attacks. There's no benefit for anyone in allowing Ukraine in at the moment, and any games pretending to do so that aren't immediately followed up with overwhelming force would undermine the treaty's actual strength. It would become immediately apparent that the Charter is no longer viewed as a sacred document and any protection for the Baltic states (e.g.) would completely evaporate. Russia would know that no one east of ASML's essential German suppliers was actually protected and start trying to grab as much as it could.

  • "the US has to accept their formal paperwork" - that's not a restriction. It's common for multilateral treaties to appoint one country to handle the paperwork; for NATO that's the US. So the "unanimous agreement of the member states" means that all the NATO members send their approval letter to the US. The US also gets to send itself such a letter.
    – MSalters
    Commented Mar 31, 2022 at 13:45
  • The rest of your mostly true statement has nothing to do with the initial false claim. Also, they may have set up some bylaws but the treaty doesn't say anything about needing a written record of the acceptance vote, only that the new member's application must be accepted in Washington by the US.
    – lly
    Commented Apr 11, 2022 at 16:55

Could NATO Accept a new member who is at war?

Yes, but the probability of this happening in the next year or so is negligibly small. For that probability to be worth discussing here, Ukraine must win the war, and Russian Federation must undergo a process similar to that of Nazi Germany or Japan after WWII (ICC, deputinization, change of constitution, substantial change of the ruling elites, free and fair elections, etc). This takes time, probably 1-10 years even under the most optimistic scenarios currently discussed by professional historians and political analysts.

There are many reasons why NATO would not want to accept Ukraine as a new member state right now. The most prominent reason being the perception that this would increase the chance of a nuclear conflict. Now this may of course be true, but we may also be wrong here.

This is 100% true, are "we" are not wrong here. NATO Article 5 must be triggered automatically immediately after Ukraine joins (see REFERENCES below). Nuclear-armed NATO will be forced into immediately striking the nuclear-armed Russian Federation. Two nuclear powers will face each other face to face. Guess what follows, please select all that apply:

(a) Nothing, except maybe a pillow fight
(b) Intense condemnation
(c) A new round of negotiations, punctuated only by poisoning of the participants
(d) Stern speech by the President
(e) Nuclear war, using tactical and/or strategic nuclear and/or thermonuclear weapons

How do you eliminate option (e). Please use the space below this answer to comment and explain.


The principle of collective defence is at the very heart of NATO’s founding treaty. It remains a unique and enduring principle that binds its members together, committing them to protect each other and setting a spirit of solidarity within the Alliance.

  • Collective defence means that an attack against one Ally is considered as an attack against all Allies.
  • The principle of collective defence is enshrined in Article 5 of the Washington Treaty.
  • NATO invoked Article 5 for the first time in its history after the 9/11 terrorist attacks against the United States.
  • NATO has taken collective defence measures on several occasions, including in response to the situation in Syria and the Russian invasion of Ukraine.
  • NATO has standing forces on active duty that contribute to the Alliance’s collective defence efforts on a permanent basis.

NATO - Topic: Collective defence - Article 5: https://www.nato.int/cps/en/natohq/topics_110496.htm

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    Article 5 must be triggered - but it doesn't specify the kind of response. NATO could, after careful consideration, decide that the best course of action is painting their parliaments blue-yellow and sending prayers. Of course that wouldn't help the new member in any way, and severely damage NATO credibility. Anything that doesn't damage credibility in such a case would bear a huge risk of escalation - which, again, would neither help the existing NATO nor the new member. Commented Mar 29, 2022 at 20:16
  • I fully agree with the risk of escalation. And the fact that there is a risk is probably reason enough not to pursue this. But I do think that the risk of nuclear conflict is overestimated. Having said that, you can not blame anyone for their unwillingness to try that out I guess. Commented Mar 30, 2022 at 3:11
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    I agree with the risk assessment and that it is unlikely, but I do not agree that Russia would need to undergo some kind of de...something...itzaton to accept Ukraine into NATO. Just some kind of peace treaty.
    – Trish
    Commented Mar 30, 2022 at 6:11
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    Point is that NATO can set any rules they want, they could just add a new rule that basically states 'we will only protect areas of ukraine that have been under Ukrainian control after the date that Ukraine joins'. Of course that still can lead to escalation, but the point is just that new limitations on the collective defence agreement can be enacted before Ukraine would join. (Not that I expect that to happen, but nothing is stopping it from happening if everyone would agree). Commented Mar 30, 2022 at 7:15
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    The problem with (e) is that neither of us can defend our position with certainty. I think that it is a believe that we can not have a war with Russia without it being a nuclear war, while you are basically claiming that it is the only course of action in a war between Russia and the US. It's probably wiser not to ty it out. But I do think that if we did support Ukraine militarily that it would not automatically result in a nuclear war. I know Putin has said it will (Or strongly indicated so), but he has said many things and much of what he says is not materializing and has not materialized. Commented Mar 31, 2022 at 6:21

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