It will start out as cyber attacks. When enough people get pissed off over losing their life savings it will go nuclear. People will demand a response, it’s human nature.
First, because nobody with nukes is going to just let themselves be conquered and slaughtered. Which is the alternative to using nuclear weapons in such a world war; choosing to die rather than strike back.
And second, because that’s been a consistent result in war games where nuclear weapons are allowed; everyone goes nuclear. That’s even more true now with the insistence in inserting “AI” into everything, because AI overwhelmingly chooses to uses nuclear weapons.
A less apocalyptical possibility (not that I discount the possibility of everything going nuclear, Og knows that the current leaders are plenty idiotic/crazy for that) is something like the Ukraine war writ large:
An spectacular beginning that quickly bogs down to a war of attrition, eventually (perhaps after years, or god-forbid decades) of that either one side collapses politically or both sides agree that it’s a fool’s game and return more or less to the statu quo ante.
IMO we can’t label anything as “WW III” until / unless at least two of the USA, Russia, and China are directly attacking each others’ military or internationally accepted pre-war territory.
In WW I & WW II in Europe, the main combatants had common land borders. The defining WW III players mostly do not. Good thing.
Also IMO, no nuclear well-armed power will allow themselves regime change / surrender without using their nukes. I say “well-armed” because I have my doubts that a country w just 1 or 2 that they’d struggle to deliver to their tormenter’s homeland would go nuke before surrendering.
One more happy thought: the more a warring country is ruled by a kleptocratic or authoritarian regime, rather than governed by statesmen, the more likely their part of the war will be conducted to benefit the strongman personally, not their country as a whole.
Massive global systems failures due to cyber attacks/counter attacks at first and then complete global destruction due to massive nuclear attackes/counter attacks….Whether Iran has a nuke or not, plenty of other nations do.
WW3 would not have the chance to drag on like the first two world wars.
Nowadays I might add the EU, or some mostly-equivalent European conglomeration, to the list of big players, but any war that involves two of those four is likely to drag in the other two, and even with only two, the end result would be the same.
Going strategic nuclear is definite possibility, but I’d suspect more as a result of misread cues than a true intent to strike first. Using tactical nukes more probably.
My WAG is a war fought calculated to cause pain but not collapse of the other side.
The problem with tactical nukes, though, is that all scenarios wargamed during the cold war were one side started using tactical nukes soon involved strategic nukes. IIRC the conclusion was that the Strategic/Tactical nuke distinction was meaningless.
As a separate matter, during the Cold War the West’s view was that there was a significant firewall between conventional weapons & chem/bio weapons, and then a yawning chasm between chem/bio and even tactical, much less strategic, nukes.
The Soviet’s published writings, and their classified doctrine, and their training, held no such distinctions. Chem / bio and nukes were turning up the lethality knob, but just a difference of degree not kind.
Which doctrinal disconnect all but assured any attempt to “signal resolve” by limited use of nukes would be utterly misunderstood even though both sides were fully aware of this dichotomy in nuclear war-fighting philosophy.
I know I don’t know beans about Chinese nuclear philosophy or doctrine. I also don’t know how much the West or Russia know about it either.