Wow really? I tried to build you a microcosm to make it simpler and that went right over your head. I gave you an aphorism from the 4th century BC about peace through power, and that too was a dud. So, lets just move on now because you aren't getting what I'm saying and I couldn't be saying it clearer.
Will explain one thing to you:
Nukes are not so much about utilizing as they are about saying I have a mother fucking Nuke bitch. Give me respect. It's worked very well for Israel, and would have worked well for Ukraine.
Sigh, and it was a stupid microcosm, neither does that quote apply. Nuclear Arms are a thing in their own. Utilizing a conventional weapon to defend is one thing but nukes carry with them huge collateral damage and an incredibly huge political cost.
Better microcosm is someone steals your bike and you send his entire family anthrax. Now if he is threating, and capable of murdering your entire family, you being able to do the same is MAD. This concept of escalation is called "The nuclear ladder of escalation" I suggest you read up on it.
It works for Israel because if they loose they are facing extinction, as a state and possibly the physical extermination of their entire people. They might use nukes as a way to bring their enemies with them.
Ill guess I'll have to walk you through it:
to my first question: Basic reason the the Crimean crisis occurring is that the Ukraine armed forces didn't really have a command at that time, they couldn't even use conventional forces. Using Nuclear forces if they were availible would not even be possible, and the escalation ladder would not have allowed for it. IE Not enough political support for using nukes.
And if they did where would they aim? At the troops in Crimea? Yeah nuking yourself is a good idea. Because that wouldn't turn 90% of the country against whatever faction made it happen.
And the international community would not accept the new regime, people all over the world would be appalled and call for removing whomever called for the strike. Plus Russia would probably declare war and they would have the political force to retaliate, because you just jumped up high on the nuclear ladder of escalation. And the west will do nothing because they cannot defend a country that just made a Nuclear First bloody Strike!
That is a loss. Ukraine is no longer a state if your lucky, Ukrainians stops existing if your are unlucky.
Nuking russia with all of your might? Will kill millions, but again in the eyes of the world no reason to do it, they stole your bike, you sent anthrax to all of their family. You loose any domestic and foreign support. International community would be against you. Russia would either retaliate with nuclear warheads and invade.
Using it in the Donbass, again same thing. Nuke one of the largest cities of the Ukraine? Yeah I don't think there really is political support to do such a thing, nor that there ever was. Again same thing, both international and domestic, there would be no support whatsoever for a nuclear strike.
Please realize something: Nukes cannot be used at a whim, because of the political ramifications they bring. Nobody believed any side during the cold war would start slinging nukes against eachothers population centers the first thing that happened. Rather it is an escalation. When you can convince people "We will cease to exists anyhow" is the only time you can use strategic nukes politically. Only when your destruction is assured, MAD comes into effect.
Tactical nukes would not work either, because then you just start the nuclear ladder. and a) Ukraine would have to nuke their own soil, and people. or b) nuke russia. That would start a war, which Ukraine would loose in the matter of days, or if using more nukes, Russia would simply bomb them back. Either way it is a huge escalation that would not realistically lead to anything but the total destruction of the Ukraine.
Since you like microcosms so much here is another one: It isn't one thief against you and both have guns. It is you with a gun vs. the national guard, they entered your home and stole something. Do you think opening fire is a good idea?
This is one of the core ideas of Hybrid Warfare! Or more truthfully it is just a continuation of late soviet ideas about limited warfare. It is a way in order to be able to use military force without the risk of WMDs coming into play.
Look at the situation today. Ukraine calls in speeches and such Russia the aggressor and senior level politicians have stated that they are invaded by the RF. Still they have diplomatic ties! That is the first thing to go!
And you are saying if they had nukes they would have used them? Get real. Nuclear War is something totally different form anything else, it is a category of its own and its theories are well known.
Ukraine having nukes would have meant squat.