Sorry for confusion. My thought was not really "Russia starts a war with NATO". I meant Russia could start a war with Ukraine and have some battles with NATO's military presence in that region. (PS: My "less than U.K" words are also not quite correct, just removed them.)

But any new member of NATO has to be approved by the current members, right? Current members have to think about what the third party (Russian) is going to react. As a matter of fact, Russian reacted strongly in the past en.wikipedia.org/wiki/…

Yes, all NATO members have to agree for a new member to join. As my answer states though, how Russia feels about a new member joining doesn't matter to NATO countries. Russia isn't in the position to tell NATO what to do, it doesn't have the leverage. As for your first comment on Ukraine, I'm not sure if you mean the current situation or a hypothetical situation where Ukraine has become a NATO member.

I meant current situation. Ukraine will probably be recognized as a "NATO+ country". en.wikipedia.org/wiki/…

"Russia isn't in the position to tell NATO what to do, it doesn't have the leverage." I think Russia does have the leverage, the natural gas.

@user24711 I don't know what that means, 'NATO+'. It seems to be an idea of some US politicians, but it's not the same as being a NATO member (because that requires all members to agree). Asking what they mean by that exactly would be a good new question though. As for Russia going to war, of course it can and it might face some NATO military forces. As long as that's outside NATO territory it doesn't trigger NATO's mutual defense clause.

@user24711 but how does gas give Russia leverage? Does it stop selling gas to Europe? Then it loses out on revenue. And Europe will just have to buy gas elsewhere (at a higher price). For example, the US has a natural gas surplus and the Netherlands stopped pumping from one of its reserves (which it could restart if really necessary). So it's not really powerful leverage, I think.

China just signed a huge bill with Russia on gas, see reuters.com/world/asia-pacific/…

At this moment the Western world fears the huge inflation. Putin is taking advantage of that, probably.

@user24711 I don't think Russia ever threatened to stop supplying gas to the whole of Europe to achieve some foreign policy goal. It may have done so to some smaller countries, but not the whole of Europe. If Russia thought it would be leverage then surely it would threaten to do this to get the West to do something Russia wants (e.g. provide security guarantees).

Not a bad answer, if a bit naïve (would the "open door" policy of the NATO be still open to China, Russia, Iran and North Korea? A military alliance is not just defined by who you decide to side with, but specially by who you're allying against), but I'll remove the last paragraph; yes, the NATO budget is much bigger than Russia's; no, that doesn't guarantee at all a sure victory for NATO, even in a non-nuclear war.

I think this answer heavily relies on, essentially, marketing materials of NATO and ignores the real-politik aspect of why NATO as an alliance exists (and how political entities actually think about their power projection and spheres of influence). Not to mention ignoring that applying policies written in marketing materials also has material effect on how other forces (Russia, China, neutral countries in EU) behave. NATO's behaviour absolutely is governed on what other forces will do. politics.stackexchange.com/a/70685/24001 seems to understand the stakes better.

@Rekesoft no, those countries don't qualify because the open door policy applies to European States, as codified in article 10 of the treaty. The article further states that the new member has to meet the principles of the treaty which include (from article 2) [a commitment to] 'the further development of peaceful and friendly international relations by strengthening their free institutions'. Those countries you mention don't meet that criterion either, at least not in the view of all NATO members.

@Mavrik NATO does not want to go back to 'spheres of influence' as we saw them just after WWII. Of course NATO doesn't exist in a vacuum, but the way countries join up through NATO is by their own choice. As for 'neutral EU countries', that's almost a contradiction in terms. The EU has its own (arguably stronger) mutual defense clause in article 42.7 of the Lisbon Treaty.

@JJJ About the spheres of influence, it seems the argument goes roughly like this.

@EugeneRyabtsev did Cuba invite Russian troops? I think there's a clear difference between sending troops on your own to a country which hasn't asked for that and sending troops when a country asks because it feels threated by a more powerful neighbor. It also seems kind of an odd comparison, the US has a minimal presence in Ukraine, most of the support is material.

@EugeneRyabtsev ... except that Cuba was never in the US "sphere of influence"

@JJJ back then it wasn't an issue for the USSR to get an "invitation" from Cuban leaders. I don't know if it is the same now, most probably is.

@fraxinus ... and does not even host an US base in there and did no trow a fit last time something was done. Things have changed since, but the abilities mostly, not general attitudes. I don't want to start a long argunent in the comments, just to explain my downvote.

@fraxinus Russia did mention the possibility of sending troops to Cuba and Venezuela earlier in the year. This article reports on the US response, it also mentions that the interim Venezuelan government was outraged but that there were no comments from the Venezuelan or Cuban embassies.

@EugeneRyabtsev I'm not sure though if any of that contradicts my answer. Is there any specific claim you think is wrong? Do you disagree that NATO is based on members joining voluntarily? I think the Cuba situation, for example, has nothing to do with NATO, it's all between the US and Cuba.

@JJJ I think I rather agree with Mavri's comment about this being a bit too heavy on NATO's marketing materials and a bit too light on the usual stuff of great-game-paying (or how shall we call it). Not practical enough.

@EugeneRyabtsev well I agree that my answer is given from NATO's perspective. I'm not sure though if there's another answer that provides a contradicting perspective. The other two answers looks at the question from Ukraine's perspective. So then you see how an aspiring member might want to join on its own free will. So I'm not sure what kind of 'great game' answer there would be. If there is such an answer, I don't think it would contradict the open door policy perspective. Can you really say it's marketing if it has been part of the treaty since the start of NATO?

@JJJ Unfortunately, I don't think I'm qualified enough to write such alternative answer. It would not contradict yours, just would target the "real motivation" vs "declared motivation", and the real is, well, real. Ukraine's perspective answers are also not really wrong, but don't mention the fact that Russia has lost non-military struggle for control of Ukraine, with successive color revolutions and all, and who has gained and now has such control. Maybe "control" is too strong of a word for the circunstances, but you get the idea.

@EugeneRyabtsev by 'real motivation' do you mean that NATO or NATO members were actively encouraging the color revolution in Ukraine? If you have evidence for that then it would certainly be (the basis for) an interesting answer. That could also contradict my answer (depending on the type of encouragement) because then Ukraine might no longer be making the choice of wanting to join NATO of its own free will. It's interesting way of considering the situation, but I don't think the evidence is there to support it.

"how Russia feels (...) doesn't matter to NATO countries" this is the crux. Noone really believes it doesn't matter to NATO countries if their actions lead to open war in Europe (of course there is already war in parts of the Ukraine).

@JJJ That, and also Euromaidan (because one time was apparently not enough). I don't have evidence about encouraging the revolution leaders (this should have been done in private), but some things have received coverage.

@EugeneRyabtsev yea the extent to which those examples were encouragement by the West versus (some in) Ukraine reaching out to get closer to the West is debatable. I don't know the specifics of those situations either. To get to the bottom of that, specific questions on History SE could be interesting. This article is an example of EU involvement as reported on here in the West.

What about the part "contribute to the security of the North Atlantic"? How exactly the countries of east Europe contribute to the security of the North Atlantic?

@convert in the same way that all NATO members do. If one country gets attacked then it can call in the help of the others. For example, when the US was attacked by terrorists and it invoked article 5 to respond in Afghanistan, all NATO members had a treaty obligation to assist. Day to day, common types of security are aerial defense and airspace policing.

@JJJ Sorry, posibly it is just my bad english, but by contribute to the security of NATO I understand, that NATO should profit from such new member or at least not geting biger problems. Since by joining the NATO east european countries have increased the confrontation between NATO and Russia and the posibility of nuclear war. How that contribute to the security of NATO?

@convert it's an interesting question. The way I read it, it means that the new member contributes to security, e.g. by contributing personnel or materials to missions. In my view, that means participating in training missions, contributing to on-going missions, etc. I don't think NATO recognizes the argument that by joining NATO those new nations decrease the security of NATO as a whole. After all, NATO believes in the sovereignty of nations and that there is security in numbers (because an attack on one is an attack on all).