I don't have one in particular in mind. I have in mind a whole pattern, going back at least as far as the invasion of Georgia in (IIRC) 2008. That said - in actions, not just words - that Russia feels free to invade neighbors if it doesn't like their policies.
Then came Russia's statements at the time of the color revolution. (No, I don't recall specific statements - that was eight or nine years ago.)
Then came the invasion of the "little green men". Russia said it was an internal thing, that Russia was not involved. Ukraine knows better.
Was that not enough for Ukraine, as early as 2013, to be looking for alliances to help their defense?
But for every move they made, Russia felt threatened by NATO. And so Russia responded by threatening Ukraine even more (mostly verbally, until 2022). But the bigger the threats that Russia uttered, the more Ukraine sought to strengthen ties to the west. This was now a positive feedback loop. It doesn't matter if one side was "right", it doesn't matter who made the first move, Russia's reactions were driving Ukraine more firmly into the camp of the west.
Since the invasion, Russia's comments have been jaw-dropping. "Ukraine has no independent existence." They threatened Finland for joining NATO. (Why do they think Finland might see the need to join NATO, after decades of non-alignment?) They threatened Poland for being a transit point for weapons flowing into Ukraine. They talked about re-creating the USSR or the Russian Empire or some big thing from the past that had a bigger land footprint. They talked about already being at war with NATO. Do they think that people don't listen to this? That they don't react? That the reaction is going to be to bow down to Russia's diktat? People (not just Ukraine) are scrambling, either toward Russia or away. Belarus is scrambling toward (Russia having kept Lukashenka in power might have something to do with that). Uzbekistan and maybe Kazakhstan are moving toward Russia. Everyone else is scrambling away, trying to find allies big enough to deter Russia from attacking them.
(Now, in fairness, since the invasion Russia has been running wartime propaganda, so of course their rhetoric has hardened. That doesn't convince their neighbors that Russia wants to live with them in peace, though.)
So, yeah. It's not just one threat. It's the whole pattern of Russia's words and actions over the last decade or two.
The invasion of Georgia followed the Bucharest summit 2008 so in my opinion this can be understood as a reaction against Georgia seeking NATO membership. Ukraine decided not to persue a NATO membership until 2014. From my initial research on the topic I arrived at Russia reacting in 2014 as Ukraine started to reverse course but other commenters have pointed out that I got the order of events wrong. They are certainly right with the official reversal with regard to seeking NATO membership which happened only in late December but I have to look into this again as I do not remember why I arrived at Russia reacting.
But I do not want to get stuck in the details of the actual events now because as you point out there is a more fundamental issue independent of the actual events. And I almost completely agree with the way you describe it as an unstable situation with positive feedback. Not sure if you wanted to say that this feedback loop formed in 2014, but if, then I would disagree. This cycle existed essentially since the end of the Soviet Union - Ukraine moves towards NATO, threats or actions in opposition, more incentive to seek NATO membership. Rinse and repeat. The specific events of course change but it is always the same cycle.
It doesn't matter if one side was "right", it doesn't matter who made the first move, Russia's reactions were driving Ukraine more firmly into the camp of the west.
With the first part I agree, but the second one is onesided. This is only one of the links in the cycle but in the same way any move towards NATO forces Russia to up their threats or even take action. And in that link it is not only the actions of Ukraine that matter but also outside actions. For example the USA wanting to support specific political groups in Ukraine in 2014 is also something that fuels the cycle as it may also move Ukraine closer to a NATO membership.
Ignoring everything after the war started because we are talking about how it started, it seems to me that everything you mentioned is related to the NATO issue, isn't it? I did some reading on the history of Ukraine Russia relations and I would say all things considered they got along pretty okay besides the NATO membership issue. Crimea is probably the biggest friction point but even there the longterm leases look like an acceptable compromise.
And let me return once more to the cycle which should have been broken long ago and must be broken at some point to achieve stability. Where can it be broken? Convince Russia that NATO in Ukraine is not a threat. Not going to happen any time soon just as a Chinese presence in Mexico would not be acceptable to the USA. A long time ago directly after the end of the Cold War this might have been possible with Russia itself becoming a NATO member. And obviously Ukraine remaining neutral or at most having only a special membership in NATO like Norway with no foreign assets on its territory.
Both have only become harder with the war and beyond that you either need radical changes like disappearing countries or become really creative. I think someone actually pointed some non-obviouse direction out to me but unfortunately I do not remember.
> Ignoring everything after the war started because we are talking about how it started, it seems to me that everything you mentioned is related to the NATO issue, isn't it?
No, I don't think so. Russia intervened in Belarus to keep Lukashenka (sp) in power, against the will of the people. I don't think the people were asking for Belarus to join NATO, though. So I think that Russia has more "red lines" than NATO. A color revolution and/or a real democracy anywhere in the former USSR is a red line, at least while Putin is in power. (Because Putin very deeply fears a color revolution in Russia.)
And I think that's the deeper point. These aren't Russia's red lines; they're Putin's. And Putin may develop other things that become "red lines", because the bottom line is "anything that Putin feels threatened by". That's not a reasonable expectation to place on other nations. Ukraine and Belarus are not Putin's playthings, nor his colonies. "Don't do anything Putin doesn't like" is not something that independent nations have to play along with.
Why should Russia have prevented a sovereign nation from doing anything? Is Ukraine not a sovereign nation? Should the US prevent Mexico from joining into a membership scheme with other nations?
Look at the US reaction towards the Solomon Islands [1] earlier this year. And we are not talking about memberships in random international organizations, we are talking about placing military assets close to rival borders. Do you think the USA would tolerate Chinese bases, tanks and airplanes in northern Mexico? What happened when Cuba asked for Soviet ICBMs as deterent against the USA trying to overthrow their government?
Sovereignty does not mean you can do whatever you want. Why do the USA and Israel try to prevent Iran from building nuclear weapons, are they not a sovereign state? Why invade Afghanistan, is hosting terrorists not something sovereign state can do if they want? You can of course maintain that sovereignty grants you the right to do whatever you want inside your territory, but then you also have to admit that not only the evil Russians are violating rights left and right.
