Looking down the decision tree, Putin might find it in his self-interest to use nuclear weapons. If given enough weapons, Ukraine might be able to resist a Russian invasion. Putin suffering a clear loss in Ukraine combined with the sanctions imposed on him might cause his inner circle to try to kill him. Putin, to save his own life, might use a strategy of dropping a tactical nuclear weapon somewhere to send a warning to the west that they better stop interfering in Ukraine and stop sanctioning Russia.
The main problem is that absent nuclear weapons Putin would lose in Ukraine because of all the support Ukraine would get from countries collectively much richer than Russia. Putin is therefore relying on nuclear weapons to win, but many in the west don't seem sufficiently afraid of nuclear war and support giving massive lethal aid to Ukraine. Some formally serious people have proposed that NATO create a no-fly zone over Ukraine.
There is this problem that giving up whenever someone threatens to use nukes, gives them an incentive to threaten to use nukes more often.
Like, yesterday it was "obviously the nukes would fly if someone attacked Russia", today it is "but maybe nukes will also fly if someone keeps supporting Ukraine defending itself from Russian attack", now feel free to extrapolate for tomorrow...
EDIT:
Problem is, this is an iterated conflict. I suppose no one here believes that a deal like "okay, Russia may take the whole Ukraine now, but then promises to not invade another country for at least 20 years" is actually on the table. (For the same reason it wasn't with Germany in 1938.)
Yes, if the outcome is "the nukes actually start flying", then we may all die. That would be very bad. But at the same time, if the outcome is "Putin mentions nukes, everyone gives up, Putin takes whatever he wants", then it is trivial to predict what Putin will say during his next invasion.
I agree, although as an American I note that Russia's conventional army is far to weak to take countries of strategic significance to the United States. Sometimes the best solution is to give in to the blackmail, especially if the blackmailer has put himself in a position where it will likely be in his interest to carry out his threat if you do not give in.
If you look at the Wikipedia page (and Wikipedia pages are generally written to support the Western elite perspective) for the agreement, the US broke the agreement first in 2013 before Russia violated it.
Certainly, this example shows that agreements with Russia that the US violates are not binding to Russian decision-makers.
Where did you hear that Belarus got spontaneously pro-Russian?
There's no claim that there's zero intervention anywhere and the agreement does not call for zero intervention. I would expect that there is not a single state that has zero intervention from the United States.
The agreement does forbid using military force and also economic sanctions against Belarus, Ukraine and Kazakhstan and the US violated it by imposing economic sanctions against Belarus.
Within a few months from that point, this then increased Russian demands on Ukraine not signing the European Union–Ukraine Association Agreement and the Ukrainian leader ruling out signing the agreement. Then partly with Western support, there were protests that toppled his government. The new government was then not recognized by Russia and Russia felt the need to intervene militarily.
That isn't to say, that Russia's actions are good. They are however far unprovoked or happen in an environment where Russia fails to honor agreements when other parties honor them.
Putin has room for not suffering a clear loss. Ukraine has a lot of incentive to agree to a deal to end the war to avoid their country being destroyed further.
If Putin thinks that he would lose on the battlefield if the war drags out, he could offer an end to the war in exchange for Donbas, Luhansk, and Crimea. Putin has enough firepower to level Kyiv to the ground if the deal would be rejected.
Putin suffering a clear loss in Ukraine combined with the sanctions imposed on him might cause his inner circle to try to kill him.
Can you elaborate on this?
If Putin thinks that part of his inner circle is against him I would expect him to rather follow Stalin's playbook than make moves for nuclear war. In many situations, preparing for a nuclear strike might send signals to his inner circle that the situation isn't stable.
As far as the game dynamics go, it's pretty dangerous for a dictator to send his inner circle a signal that the dictator believes that he has only a 30% chance of success because that means that his inner circle has to plan for securing their power in the absence of the dictator.
One of the worrying aspects is that the situation has not developed in the way many (most?) people expected earlier. (But note that I'm far from an expert on Russia, or Ukraine, or war, so maybe I have the wrong impression here...)
Before the conflict heated up, I and many other people expected that Russia would just try to grab the eastern part of Ukraine, where a good part of the population would welcome them. And Putin seemed to be following that script - support local insurgents (already done), then declare that their separatist regions are independent countries, then say you're sending "peacekeeping" troops there at the request of these new independent countries - all seems designed to separate these parts from Ukraine, at which point these new "countries" ask to join Russia...
When there were reports of attacks further inside Ukraine, I wondered whether Ukraine has tried to stop this plan by attacking the Russians in the east, and that the Russians were simply neutralizing Ukrainian military assets that might be used against them.
But it's now obvious that the Russian plan was always to conduct a more general invasion of Ukraine. A big reason for worry is that it's hard to see what Putin is trying to accomplish by this, unless it's part of some highly dangerous larger plan.
The other reason for worry is that some people in the West who ought to know better have advocated insanely reckless responses, such as sending NATO planes to shoot down Russian planes in Ukraine. It's not hard to see the Russian response to that being to bomb the NATO air bases where these planes are based. NATO then responds by bombing Russian air bases... It probably doesn't end well.
But it's now obvious that the Russian plan was always to conduct a more general invasion of Ukraine.
Actually, Putin made his plans quite public some time ago.
This is the funny thing where Putin may literally publish an essay on his desire to invade Ukraine... and yet many Western intellectuals will continue saying "no, that is not true, that is American propaganda, you are too smart to believe that aren't you..."
A big reason for worry is that it's hard to see what Putin is trying to accomplish by this, unless it's part of some highly dangerous larger plan.
This sounds alarming, yes.
I don't think there's much mystery to Putin's intent. Desired outcome is pro-Russia Ukraine, and chosen method is decapitation by rapid advance to Kyiv followed by regime change. Actions so far are consistent if resistance was expected to be (as many in fact expected) Crimea-level or Afghan-level.
I think you may underestimate the power of an oppressive regime.
If you kill all people who publicly oppose Putin, most of the remaining will follow their survival instinct and develop some version of Stockholm syndrome. For those who won't, there is still the police and secret police to eliminate them later. And you can always resettle some people from Russia to Ukraine and vice versa.
The primary danger is a nuclear war. Putin has ordered to put nuclear forces on high alert, and that's enough. It's analogous to Cuban Missile Crisis, and that was pretty dangerous.
Otherwise, it is not particularly dangerous. World leaders seem pretty careful to avoid escalation so far. There are lots of reactions due to high saliency (as you mentioned, close to Europe etc, compare Georgia), not due to high danger.
Potential danger is that due to war's "popularity" (a bad choice of word, but can't think of better ones off the top of my head), leaders of democratic countries may feel forced to escalate, because they are ultimately accountable to people. It is their duty to say no to escalation, but they will be tempted to say yes.
I think the most obvious reason is that Putin has said:
The claims that Russia is itself threatened (or is claimed to be to justify actions) is the main difference here I think.
A radically oversimplified background:
After WWII, Europe was divided into East and West, with the West being the American sphere of influence and the East being the Russian sphere of influence. On account of the Soviet Union being communist, and supporting communist revolutions in all of Eastern Europe, tensions rose considerably. The outcome of all of this was the division of Europe into NATO and the Warsaw Pact. These were both big, complicated military cooperation agreements but at their core they were mutual defense treaties, which in the NATO's case is specified in Article V: an attack on one shall be considered an attack on all.
The military situation was this: the Soviet Union was the most powerful country in Europe by far, and in tandem with the Eastern European powers had an overwhelming advantage in a land war. This is because the only power which could compete with it was the US, and there was no way to move the entire US Army to Europe in time to make a difference. This introduces a problem of how to make US air and naval power important, and it was determined that the cost of maintaining sufficient forward operating airbases would be ruinous. However, at the end of WWII the US is the only nuclear power; so the threat is that if the Soviets invade, the Americans will use nukes. Enter deterrence.
The Soviets develop the bomb in 1949. This is the same year NATO is formed, and the joke in diplomatic circles is that it had three objectives: keep the Americans in, the Russians out, and the Germans down. So now there is a problem: while the Americans can use nukes to deter conventional invasion, the Russians can use nukes back to deter first strike, and to make a rich and varied story short and boring both teams spent the next 25 years building up huge stockpiles and various delivery systems to ensure that each side was guaranteed the ability to hit the other with nuclear weapons. This culminated in a doctrine of Mutual Assured Destruction (MAD): both sides were guaranteed the ability to destroy the other.
This is the part which is germane to your question: at one point the US and Russia had both pre-committed to extinguishing all of civilization if either were to attack the other. So strong was this commitment that they both refrained from taking significant defensive measures (mostly). They built automated solutions to ensure armageddon would still happen even if all of leadership were destroyed. For a long time, the way of the world was that if the US and Russia went to war it was the end of the world; and if any NATO country and Russia went to war it would mean the US and Russia went to war.
The Russia-Ukraine issue is just the sort of event that began WW2, and also that spreads into a broader regional war. But a regional war in Europe means US v. Russia, which is the most terrible fear in geopolitics.
Mind you, lots of things have happened to make the nightmare scenarios less likely; but also lots of things have happened to make medium-grade global catastrophes more likely.
While I lived through and can confirm the prevlance of the 'extinguish all civilization' MAD narrative, I wonder today how extinguished it actually would have been. (famine due to a year of reduced sunlight from dust floating around was part of the story)
"at one point the US and Russia had both pre-committed to extinguishing all of civilization if either were to attack the other."
Do you have a reference? Which time in particular are you thinking of? My recollections are that at least from the 1970s on, US doctrine was to hit only militarily significant targets. Of course, millions of civilians would die as a side effect, and perhaps civilization would end in some sense, but it was not an explicit policy.
If everyone acts rationally, the result will be Ukraine growing closer to the EU, Russia becoming more isolated, and no WW3. But Russia isn't acting rationally, I'm losing count of distinct stupid things it has done since Feb 21. Extrapolating that stupidity into the future makes me think that WW3 is quite possible.
If everyone acts rationally, the result will be Ukraine growing closer to the EU
I am curious why you think that.
To avoid provoking the Soviet Union, Finland and Austria refrain from joining the EU till 5 years after East Germany joined the EU and they still are not (and never were) members of NATO. Nothing bad happened to Finland and Austria that is a quarter as bad as what is happening to Ukraine now.
I'm not some kind of geopolitician, but I see a number of obvious reasons: this is a full-fledged war in Europe between two large countries; NATO countries clearly support Ukraine with everything, but do not send troops because Putin threatened with nuclear weapons; many expected that this war would not happen, because it is obviously a dangerous and not profitable move, so now they are not sure that there will be no attack on a NATO country or a nuclear strike.
And what would be the key difference with the wars in the Balkans in the 90's? Their sheer size? The GDP/capita of Russia and Ukraine is very low. Or that these were independence wars instead of wars between countries?
Putin will sweep all the way to the Atlantic if he is not stopped. The best time to say no is always right now.
There are plenty ways of saying 'no' that can escalate toward nuclear war.
The best ways to say 'no' are those that have precommitment toward them. Both NATO and the EU are precommited to defense of their borders.
Apart from that the Russian army already has a hard time fighting the Ukrainian army. The idea that it would have the power to push through the Atlantic seems very far from reality.
I have heard that since WW2 there have been ~140 armed conflicts in the world. Only few of them have been full-fledged wars, let alone big ones. However, as I don't know almost anything about wars and the politics around them, I cannot really formulate why this war is particularly dangerous and prone to start WW3. This one is specially frightening for me because it is very close by --I'm European--, but this does not make it more prone to e.g. start WW3.
I have thought of few factors (location, countries involved / potentially involved, possession of nuclear weapons...) but the war in Ukraine does not seem to be too special in any of them. Is it maybe the combination of factors what it makes it particularly dangerous? As many may, like me, not be too versed in geopolitics/geostrategy, I think it would be useful to compile a list of key factors setting this war aside from all the other wars the world has endured since WW2 and making it particularly dangerous for the whole world.