I realize I may get some divisive answers, but if NATO Countries all agreed, mobilized, and went into Russia full force with no warning, what are the likely outcomes?

Nato would completely overwhelm Russia, but not before nukes would fly from various places and hit major cities in the western world. In the retaliation, all of Russia would be destroyed, world in turmoil...
- I have some doubts that Russia's nuclear weapons are even in operational order.
  maybe they try to launch them, and they just self-destruct inside their silos. or, they fly, but fall out of the sky still in Russia, or, they actually fly all the way to the destination, but fail to detonate.
  to be sure, this is not something that we should wager on. I just think it would be funny if it turned out that way. just a fun little daydream of imperialist fascist scum getting put in the ground where they fucking belong.
  
  Russia is believed to have about 6500 nuclear weapons. Even if ninety-nine percent of them fail, that's still 65 cities turned to ash.
  
  You don't have to take Russia's word on it. USA and Russia inspected each other's nuclear arsenal as part of the New START treaty until the beginning of covid.
  
  They have considerable overkill, to the point where only a fraction has to hit their target.
  
  The imperialist fascist scum would be launching the nukes from the safety of their elaborate, well-stocked, and expensive bomb shelters. I don’t disagree with your opinion of those people, but it’s vital to remember that the biggest victims would be the millions of civilians who have already suffered under their rule.
  
  Even failures could be bad, for nearby areas or the world. Just a missile falling and then burning is going to release stuff into the air and water. A far cry from a working launch, but still a mess and that's just one missile. What is the probability that they all fail to even launch or just do something and crash inert? Not big, I would guess. Even a badly maintained nuclear arsenal has its own deterrence.
  
  The IAEA and the START treaty mean we have inspectors that can monitor the actual capabilities of Russia's nuclear arsenal. According to these inspectors Russia has, at least, 2000 completely operational nukes.
  
  No one is willing to bet the existence of human civilization on that.
  Even 2-3 working nukes (out of thousands) would destroy dozens of cities (they each carry multiple warheads that split up in space).
  And it would still trigger a retaliatory strike that could cause a nuclear winter.
- Russia has 5000 nukes, if the US is not involved, Europe will be toast
  
  NATO would ensure that the US is involved. We're aligned with the Europeans.
  
  Even without US. UK has nukes, France has nukes. You don't need a lot to destroy Russia. Basically just two.

nuclear war

There's a problem with your premise. NATO (much like the UN) is not a military force of its own. Rather, it's an agreement between many nations, each with their own militaries. There is no NATO army. There is an agreement of the United States (with its army), the UK (with its army). Germany (with its army), etc.
Each of them could independently invade. They could even negotiate an agreement to invade. But that would have limited impact on NATO. The big thing would be that any invading country loses the agreed upon defenses of the rest.
- That’s rather pedantic, but I guess it’s a valid point, so I clarified my question to mean what you already know I was asking.
- Technically, NATO has multiple multinational battalion battlegroups at Russia's border in Poland and the Baltic States, although they consist of only a couple of thousand soldiers.
- Well, the armies have standardised a lot of things and train together, so they very well can act as one army

Do you like tablewear?
Because this would create a lot of glass in a few short moments.
- Took me a sec to realize what you meant by this lol

Assuming no one nukes the world or that all air defenses work, it’d be a mess. There’s no force in human history that can stop NATO in a traditional war. (Maybe the Mongols because they’re always the exception.) But it’s very likely China, North Korea, Iran, and others would be much harder to conquer/occupy at the same time.
It would be widespread suffering in most of the world. The truth is that war is obsolete as a means of accomplishing 99% of political goals. Most of the world would descend into chaos and civil war. Food would be scarce and in times of scarcity, the drunkest, most violent people usually end up in charge. You’d have warlordism in the vast, vast majority of the world.
The natural state of humanity isn’t trade and property rights. It’s warlords offering protection in exchange for whatever they need. No one “wins” wars in 2024. Groups like ISIS would thrive, not law and order.
- What makes you think humanity has a natural state?
  
  Yeah, I don't think we've had a real "natural state" since we discovered agriculture. Our whole thing is kinda setting ourselves above/apart from nature
  
  Like I mean after Rome fell the kingdoms that arose were pretty warmongering picking fights with other kingdoms for mearly having a different religion and even when Rome was a thing capital punishment was pretty common and brutal and Rome was a super power for being military strong nations only really started to be widely civil to one another by id say 1880 somewhere in the late 1800s leaving about 1,850 years of constant wars between all nations
- Easy way to kill a country: Disrupt the critical infrastructure at multiple points.
  Just imagine how crippled we are without AWS, Azure, Cloudflare and Gcloud. Kill electricity, damage water supplies and destroy medication supply and the chaos is perfect.
  
  "Without their heads, they're powerless!"
- Wait I'm confused. Why would a NATO invasion of Russia destroy the rest of the world? Sure, Russia would be fukd. And if China tried to defend Russia for some insane reason, it would be one heck of a war. But not "entire world falls into anarchy and chaos" levels, that's absurd.
  
  I think the assumption is China would join in with defending Russia for fear that it would be next and alone. I’ll edit this and add Iran to the assumption that they don’t want to be next and alone either.
  China clearing wants more resources and land. China has historical ambitions in Taiwan. China has historical grievances with Japan.
- Gotta think of the Mongols.
  
  As long as we're living in the past, let's revive the golden horde to deal with Russia
  
  It's kinda sad to see Mongolia now. Not a lot going on, almost completely dependent on China.
- Vote for me as your warlord plz!

It's nearly impossible to mobilize a large force quickly, or covertly. There would be plenty of warning, especially if the US is involved because there's an ocean in the way in either direction.
If Western nations decide to attack Russia, I doubt the conflict will stay limited to Russia.
North Korea will probably support Russia militarily very quickly. They're already supplying weapons, they have a close relationship, and they're reasonably secure against counterattack because China would react very badly if NK were attacked directly.
Iran will join with Russia, but uncertain whether Iran will actually deploy its military in Europe (probably not), or take the opportunity to pursue their own goals in the middle east while the west is distracted.
China will probably play neutral for awhile, but continue to trade with Russia and sell them military equipment. China is circumspect, they won't jump into a conflict for ideological reasons, though they'll certainly quote ideological reasons in their propaganda. They will join the conflict when it benefits them and doesn't present extreme risk. Most likely they will pursue their own goals in the south China sea (Taiwan, Malaysia, the Philippines) while the US is busy elsewhere.
An attack from the West on Russia will balloon into a global conflict. It will be bad for everyone, even if it stays limited to conventional warfare.
- I agree with your prediction of China’s behavior (and especially their motivations) 100%.
- It will be bad for northern hemisphere *
  
  Aside from the global environmental and economic fallout, I imagine many Southern Hemisphere countries would be dragged in as well.
  
  This point of view is at best myopic.
  A more complete description would be ignorant, narrow-minded and reckless.

It is a complete crapshoot because it all fepends on whether thechain of people between Putin and the missles are more interested in going out with him.
What I expect to happen with an invasion:
NATO invades and quickly disables a ton of Russian military objectives. This is because Russia is already flailling with Ukraine due to lack of discipline and outdated tech that theybhave mostly lost already. Plus they can't do waves of conscript tactics at a moment's notice.
Putin loses it and tries to launch the missiles knowing it is the end of hos time in power. His military advisors refuse the order and stage a coup, killing Putin and blaming NATO, then fight a half hearted conventional defense for show before negotiating a ceasefire.
But that is just my thought and the risk of a nuclear launch makes it a terrible idea to launch a surprise invasion as some nuclear sub might respond tonthe invasion if their cummunication is cut off.

Considering that Ukraine is advancing inside Russia without so much problems, probably bad, for Russia
- If Russia uses nukes, Russia, the state, will cease to exist. The Oligarchs know this, Putin knows this. Only an existential threat to the Oligarchs and Putin would result in a nuclear strike. And that's why there was no nuclear response to the Kursk incursion so far.
  
  If NATO invades, Russia is doomed. Putin doesn't care that Russia would still exist after a NATO victory, all he cares about is himself and his legacy. Both of which would be destroyed in a NATO victory.
  So he would launch the nukes and watch Russia get wiped off the map, because if he can't have it, no one can. And at least he would go out with a bang, rather than suiciding in a bunker.
  The oligarchs would not be able to prevent it. They might hold the political power, but the military order to launch the nukes comes directly from Putin. The best we could hope for is conscientious officers refusing the order.
  
  In addition It's also not a good idea to nuke a place you intend to occupy.
  
  If Putin get shoot in the head?, the oligarchs don't like him, and there's a gigantic amount of people wanting to get his place

Pakistan and India have enough nukes to cause major famine across the world. Russia alone has enough nukes to nearly if not surely end humanity even if only 1% of the human population were killed directly from a nuclear explosion. I think the only way NATO could take Russia is if they were to somehow disarm their nukes.
Also, we have to consider alliances. Russia and North Korea are closely aligned. If the entire world went to war with NK, it is still possible that South Korea would be devastated because they have setup their entire military to shell the fuck out of South Korea at a moment's notice and have an extensive underground tunnel system for retaliatory purposes. However, it's possible that NK would value self-preservation over maintaining it's alignment with a Russia that will definitely not exist anymore.
- Not to argue, but shit hitting the fan on this scale makes loyalties much harder to predict.
- That depends on how well maintained their nuke arsenal is. I can see a couple launches that will be shot down but other countries would not rick nukes for the sake of Russia.
- I wonder what would be required to surreptitiously disable most or all Russian nukes
  
  what would be required
  The Russian government.
  
  Well the good news is that we do have some ballistic missile defence in place. The bad news is that we don't really have enough of it. We could probably shoot down a couple hundred nukes... I'm highly doubtful that we could shoot every nuke out of the sky, if Russia decided to unleash everything they had.
  
  I'm imagining some sort of three-pronged strategy. One, espionage to convince people in the nuclear chain of command to disregard any orders to fire nukes. This would involve converting people that have likely been thoroughly vetted by the Russian government. It would also be risky in that all it would take is for one person to snitch for the Russian government to catch on.
  Two, a cyber attack that disarms nuclear weapons firing systems. This would likely involve gaining physical access to many launch systems, infecting their computer systems, then letting the infection stay dormant without getting caught yet somehow activating it when necessary. Say for example they run a dummy drill without nukes, the infection could be discovered.
  And three, a interception system for nukes that are launched. This would be the most risky because it would involve intercepting nukes immediately after being fired. For ICBMs, we'd have to get them right after launch since once they're in space, it's nearly impossible to intercept, especially after the warheads separate from the rocket. Submarine-launched weapons might be easier to intercept if they're strapped to a rocket until detonation. Bombs would be nearly impossible, but it would be a lot easier to intercept the planes they're on.
  Overall, I would guess we'd be able to stop some Russian nukes from hitting NATO targets, but not all of them. It would be a wild guess to calculate the percentage that get intercepted/through. Russia has about 1,710 nuclear weapons deployed. Let's say they fire half of them as a retaliatory strike saving the other half as defense in case the retaliation stops a NATO attack. If only 1% of that half make it through, that's still 85 8.5 nuclear strikes. ~~If only a 10th of that were aimed at major cities, that would be 8 major NATO cities that are obliterated and then require major recovery efforts.~~
  Not one country is prepared to recover from a nuclear strike because that's virtually all natural disasters in one. Imagine the devastation if London, Paris, Berlin, Rome, New York, San Francisco, Washington DC, and Los Angeles. There would not only be major loss, but the rest would have to dedicate immense resources to helping those areas recover, further pulling resources away from defense and counterattack. ~~We would also have to consider that the other 75 nukes attacked infrastructure and military targets, so we'd be severely incapacitated.~~
  tl;dr: stopping and surviving a Russian nuclear attack is practically impossible

Nuclear annihilation. Got nothing to lose at that point

In a conventional war they would crush Russia. Remember when the United States captured Baghdad in a week? It would be like that. But the chances are high that Putin would start launching nukes, and then everyone loses.
- I'm not willing to gamble but I don't think they'd go nuclear. The trick is to offer amnesty and support to everyone but Putin so they have a better option than death for themselves and their families. Loyalty to dictators is always about self preservation.
  
  They would drop tactical nukes on NATO forces.
  It's never going to happen anyways.

I think it's more likely that Nato would quickly just storm the occupied regions of Ukraine. Would probably be less risky of a nuclear Armageddon
- I am down with this idea

The End of the World
- But I am le tired!
  
  WTF, mate?
- The end of the northern hemisphere*
  
  Well, nuclear winter would certainly solve that global warming problem for everyone left.

A lot of people are focusing on what Russia would do but this would also alarm every single country that isn't in good terms with NATO and they would also start mobilizing their armies. China, NK, and maybe even the middle east would retaliate if nato was this aggressive.

into Russia full force with no warning
That is wrong on so many levels.
Unthinkable.
No more than a wet dream.

Because Putin is a “So much for your fucking canoe!” kind of leader. I think most world leaders are if they have the chance. Look what we still say about France for surrendering in WW2, they get plenty of mockery despite being the very nation that helped the US exist in the first place.
So the default is that the worst of the rich and powerful like Putin have the relationship with their citizens and country that a narcissistic, severe domestic abuser has with their partner:
“If I can’t have you, no one will…”
(Canoe ref if you don’t know it, sorry for the shit site)

Short answer: the end of the world.
The resultant nuclear war would kill a good portion of Earth's population, but it's likely far more would die from the chaos of civilisation being instantly forced back to the iron age by the EMP frying every silicon transistor.
- I used to be a Boy Scout. That just means I’ll die a bit slower.
- For anyone interested in some light fiction on the subject, may I direct you to On the Beach by Neville Shute.
  
  The film Threads is also relevant.
- The end of the northern hemisphere*

kinda depends on what china would do.
china is one of the only reasons russia is still standing on their feet. if china wanted, russia would be out of ukraine tomorrow.
nato vs china is ww3

Eric Schlosser's book, "Command and Control" may be of interest to you. I found it hard to put down.
Daniel Ellsberg's book, "The Doomsday Machine" might come closer to answering your question, but I have not read it.

what are the likely outcomes?
Putin launches nukes, huge amount of civilians die, russian military is crushed within next few months. NATO wins at the cost of horrible loss of civilians killed by russian nukes. World economy shrinks considerably
- So, this is the same analysis I read like a year ago. Do you feel that the current situation is not different enough now to indicate an alternate course of events?
  
  Do you feel that the current situation is not different enough
  Putin has the exact same number of nukes and ICBMs as before. This is the main factor, and I don't see it changing any time soon
  
  I’m not who you asked, but I’ll answer anyway: no

For more humorous (but still serious) answers try asking in !noncredibledefense@sh.itjust.works
- I’ve never posted there, but damn I’m glad I found them. Highly recommended.

https://www.youtube.com/watch?v=pklr0UD9eSo

About those nukes…
- I'm sure they were kept at the same tip top condition as the rest of the russian military complex's equipment.
  
  Possibly. But even if 99% of their strategic arsenal is junk, they'd still be left with 17 working warheads. Who's gonna risk 17 large cities wiped out?
  
  Poorly maintained nukes, that make me feel better, thanks

I haven't been paying to much attention to the news but I've heard that other, non-NATO, countries have threatened some of the countries that are just simply giving aid to Ukraine. So, I'd assume that those other countries would get involved in some way and just make things worse for everyone.

Ukraine has no nuclear weapons. Nuclear arsenal is basically meant to face nato/USA in Russia.
Ukraine invading Russia is a humiliation. But it's not a real threat for now. Russia didn't even declared the state of war yet.
I've heard that Russia can't really use atomic bomb against Ukraine because Ukraine has no atomic bombs itself. If it did, it would spark nuclear proliferation by breaking a tabou. And China wouldn't allow that, because they don't want Taiwan to get the bomb.
But nato is an atomic power. Thus, atomic bombs are fair game.

This will be a popular song for the 15 mins it will take for the missiles to reach their destination.
- Also Tom Lehrer's take

World war III and after that NATO countries occupying Russia. Probably quite some people die and things get destroyed in the process.
I think if they're smart they destabilize the regime and go for Putin. And not fight the whole country and population of Russia.

For starters: amassing troops at the russian is a warning.
But I think a coordinated attack by NATO could neutralize all russian air power, at least in the western part. Thus preventing Russia from waging war in Ukraine or making any attacks on NATO countries in return.
Nuclear war is not plausible due to Mutual Assured Destruction.
- If your destruction is already inevitable because all of NATO is invading your country, then mutually assured destruction begins to look like a good option from the losing position.
  For this reason I would argue nuclear war is plausible in the scenario.
  You may also say "well the NATO forces may be looking to arrest you and not kill you so logically your best bet is to hold off on nukes", but people, even leaders of countries, often don't react rationally under extreme circumstances so there is definitely a non zero risk of nuclear destruction.

Russia is obliterated shortly followed by Russian nukes shortly followed by the end of humanity as a speicies.
- the end of humanity as a speicies.
  Now that would take at least some more months. And they are not exactly fun months.

Everyone I've read here is talking about Russia immediately launching their nukes, but among so many nations, surely several would think to do something sneaky to disarm the nukes before anyone launches a full-on attack against Russia.
- If any nation could build an intelligence network that can disarm all 4000+ nukes inside Russia and can coordinate it before an all out attack; at that point they could push a puppet leader to control the country anyways.