It’s only rational to start a nuclear war if a country faces a direct existential threat: i.e. a significant percentage of the population will be killed or conquered and enslaved. The perceived outcome of nuclear war (widespread devastation) has to be preferable to what would happen otherwise.
Conflicts over territories at the far fringes of a great power’s sphere of influence (or desired sphere of influence) obviously don’t meet the bar. If it’s trivial to call your bluff, it’s probably better not to bluff.
The logical consequence of disagreeing with this is that every country that doesn't want a significant percentage of their population killed or conquered or enslaved should get their own nukes, because nobody else wants them. And I'm not sure every country acquires nukes is a safer world than maybe we don't let Putin have everything he wants
He knows it would be strategically impossible for the US or Nato to respond in kind to a nuclear attack on Ukraine. It can be rational for him to climb the escalation ladder if he knows his enemy will have to back down before he does because they have less to gain and more to lose.
I don’t like this situation at all, and I understand the point about rolling over to threats. Unfortunately, this is just how nuclear game theory works whether we like it or not. You can’t win in a conflict under MAD against an opponent who has more at stake than you.
And of course there can be an advantage for Russia in using nukes. They could destroy Ukraine's entire army, kill all its leaders, destroy all its infrastructure, etc. with no risk of (nuclear) retaliation. There would be many negative consequences too, so it's not likely to happen unless the conventional war is going very badly for Russia, but it's certainly a card they hold.
Putin doesn't know that. Putin doesn't know quite what the repercussions would be. That's why he hasn't used them so far.
The reason the EU countries don’t just waltz into Ukraine probably has more to do with the knowledge they’re not dealing with a rational person, but with a bunch of ego. It’s not hard to predict how Putin will respond if his ego is threatened, but how the rest of Russia will respond to the command to launch nukes.
It’s not unlike the US, except it’s currently still fairly easy to predict that any US commander will just say no when ordered to fire on the EU.
(I expect a first response would be a single city, with warnings to evacuate. A show of what's next.)
The goal would be that Russians assist in taking out an out of control, lunatic who will destroy us all.
Understand, this isn't just about today. Over the next 100 years, every country will obtain the capacity for nukes. Every person on this planet needs to see, and know that using them indiscriminately means you lose.
The consequences are too dire otherwise.
And when a US city is taken out in response? Do you keep going? Over a country that ultimately has very little impact on the US?
Your premise is basically that US military leaders are irrational to the point of insanity.
This isn't a game you win by backing off. There is no safety in that move.
Understand, the claim that the Ukraine is "Russian" is an absurd bluff. No one truly believes that, not Putin certainly. There are a dozen other countries in that region that Putin could make the same bluff about.
By allowing this bluff to continue for this long, matters have only gotten worse. We allowed 2014 to happen. Now, we're here. It won't stop a a peace agreement, or at Ukraine in whole.
The insanity is Russian. And you don't leave a rambling, insane man with a gun outside your house, shooting randomly at houses, because they're not quite at your doorstep yet.
The game theory works roughly like this: Putin wins the most if his threats work. If they don't work, he has the choice between drawing a new red line, launching a limited nuclear attack on Ukraine, or full-on nuclear war. The last option is obviously out (guaranteed destruction is in no proportion to the reward). A limited nuclear attack would likely make him a pariah on the world stage and make it even more difficult to find trading partners. So instead he redraws the line.
If he ever went for the limited nuclear attack option Ukraine might give up, and the west would have to choose between war against Russia (high risk, low reward) or just tightening economic sanctions to the max and punishing anyone who dares to trade with him.
If we assume rational actors I don't see how this would ever escalate to nuclear war. And as long as Ukraine doesn't find a way to decisively push Russian troops out Russia has no incentive to climb the escalation ladder. Even as prolonged war leads to internal instability
Ukraine can cross as many of Putin's "red lines" as they wish. Ukraine did not start this war.
That's purely a psychological trick, if you take this as true then it would be rational for everyone to place madmen in the negotiating seat. A better example, if I had Trump say to China, if you don't open up your markets and drop your tariffs on us, we will nuke you. If I can guarantee as thought exercise that Trump will fire nukes if demands are not met (and that's not difficult to do in reality), do you think Xi Jingping will concede here?
That’s, again, the whole problem. You don’t have to view Putin as “mad” to see him taking a nuclear last stand over Ukraine. He is already invested and taking risk at an extreme level to the point that no one can doubt the importance to him and his willingness to make heavy sacrifices to win. There is no believable narrative where a US leader would be willing to gamble at an existential level over Ukraine.
But what if Putin thinks that unless he takes Ukraine, Russia will cease to exist (or Putin will cease to exist). In that scenario, taking Ukraine is an existential goal for Russa, and he will blow up the world unless he wins.
Unfortunately, I think the rational thing to do is to apply increasing pressure to Putin until he either backs down or proves that he is willing to blow up the world over Ukraine. If the latter, then we back down. Of course, the risks of that strategy are all too obvious.
Russia's nuclear arsenal is a perfectly adequate guarantee of Russia's security. Putin knows this, which is why he's happy to leave Russia's western border with NATO practically undefended while he pursues Ukraine. (This also disproves the "Putin invaded Ukraine because he's afraid of NATO" lie.)
It's more plausible that Putin's survival depends on the outcome of the Ukraine war. But "mad Putin blows up the world" is as much a problem for the Russians as anyone else.
That's also the reason why Alaska and France are safe, why Iran wants nukes, and is the best argument against disarmament you can find. The cat is out of the bag, and the attempts to put it back are starting to leave scars.
Because every time it is brought up it is easily demonstrated that nobody actually agreed to defend Ukraine. They each agreed not to invade Ukraine.
The only assurance of assistance built into the agreement is that parties would complain to the UN security council.
The Obama administration let Russia violate the agreement when they took Crimea. Putin's justification that Ukraine isn't a nation but a historically Russian territory only works if Russia pretends it was never a signatory, since recognition of Ukraine as an independent and sovereign nation was a part of it.
In short, pieces of paper do not trump the fear of nuclear weapons.
So? If nuclear war is always an intolerable choice for America, then America's nuclear weapons will never be used in any case, and any aggressor who can plausibly threaten nuclear war is free to seize anything from America with that threat.
If nuclear war isn't always intolerable, then, well, we've eliminated the premise off the upthread argument about Ukraine, and are in a different discussion.
Had Russia invaded a NATO country, we still would not have launched first, but rather used conventional weapons, given the fallout (literal and metaphorical), but actually using them to prevent greater numbers of casualties from protracted war is not fully off the table, so to speak.
As soon as you decide this, and let others know you have, you have lost everything. Because if that logic applies to Ukraine it applies equally to Poland, to Alaska, France, to Washington, D.C., to your hometown. You've committed to surrender everything to any power that has the potential to escalate to nuclear war.
(It's even worse if you don't believe this -- or if you think you do but would think differently if the thing to surrender was closer to home -- and let people think you do, because that makes it almost inevitable that things will escalate beyond your trigger point, resulting in nuclear war.)