This in a early cold war era US vs USSR Armageddon scenario, not a 202x scenario.
Plausible scenarios today are:
- Russia using a nuke in Ukraine and earning the hate of every single country in the world. China and India try to remain neutral but they would almost certainly drop support for Russia if they break the nuclear taboo. This would not even require a nuclear response to solve.
- Kim doing something stupid.
If putin keeps the radiation from spilling into nato territory its not enough to start ww3.
Despite cnn's lies, nato doesn't actually care much for ukraine, they just see this as a way to do damage indirectly to an enemy they want to hurt.
Nato isn't interested in committing suicide, afterall nuclear war benefits noone.
Honestly I see the ukraine situation either ending with a discussion that cedes at least the 2 "republics" on the border, or small yield nukes being used on small targets to scare ukraine to the negotiation table.
The reality is russia can last enough in war but ukraine is pretty tough and has nearly the same if not even more men than russia fielded.
they will almost certainly negotiate.
I think the avenues for retaliation from the world are far more diverse but retaliation of some kind is almost certain.
This is the reality of the "Assured Destruction" of MAD. If you can take out your enemies ability to respond you can "win". With a tactical nuke in play and Rus-vs-US force engagement moves us to DEFCON 1. The name of that level is "COCKED PISTOL". A cocked pistol is something to handle gently, any wrong nudge could set it off.
Then in the background you have air to air engagements over the Black Sea - blockades of Kaliningrad, SSN's chasing SSBN's. Dozens of Cuban Missile Crisis type situations all playing out in parallel. One bad call by one local commander and a head of state is given 6 minutes to figure out if this is a first strike.
Once the line is crossed almost all of us die. It might take hours, days or weeks - but it will be an near inevitable conclusion.
That is virtually impossible. You can count on at least some detectable level of radioactive fallout reaching a NATO country. That could be enough to trigger Article 5 IF the political leaders of NATO willed it.
To really simulate this sort of scenario properly, you need political wargaming (e.g. matrix games.) And the best way to do that is with politicians themselves, or at the very least members of their staff, participating in the wargames. This isn't the sort of thing you can simulate properly with computers or college students.
Where do you think that would end?
Such a strategic situation would be incredibly unstable. If no retaliation comes, the madman will think he can use the same gambit to take the Baltics and other areas. He's been at this since Chechnya. There's no way he'll stop his aggression and violence unless someone stops him.
The only way to stop this is to effectively deter him from using them in the first place. And the only deterence is to credibly threaten immediate nuclear retaliation.
The problem with disarmament seems to be that imbalances arise, and the problem with armament seems to be that if hundreds of countries have them, there's a high probability of one of them doing something stupid/crazy/suicidal.
The only way I can see Russia going nuclear is if the West becomes directly involved in the conflict, Putin sees it as the existential end of Russia, and decides to take the murder-suicide route. Let’s hope it never gets to that point.