Two things:
- US allies totally have nukes. Hell my country officially has no nukes, but unofficially we have a couple of US-owned nukes stored away. France has nukes, UK has nukes.
-Total global nuclear war is something that humanity won't survive, and your scenario change is actually making it harder.
Basically, if the Cold War went hot, the northern hemisphere would be totally fucked. Both parties had tens of thousands of nukes, and thousands of them ready at a button push. Infrastructure would not survive. But the southern hemisphere would be largely unaffected. Now, climate change (e.g. nuclear winter), the disruption of trade and such would heavily affect them and plunge the world into chaos, but they would reasonably survive.
Furthermore, whoever would rise from the ashes would be the defacto world superpower, and if circumstances permit (as they have in history), could easily come to dominate the world. Western hegemony in part is due to a lucky combination, giving europeans both the drive and means to conquer the world. In the case of a post-apocalyptic world, exerting control would be essential to obtain all the necessary resources.
Now of course you specified an alien planet, but the logic still holds: The old order can blow itself up and a new order can rise from the ashes, and due to the imbalance of power, becomes a World Order (also because half the planet would be a nuclear wasteland, so it's more of a One/Half World Order)
As to how long it takes for the dust to settle, that's a very difficult question. It depends on loads and loads of factors, such as how much dust and where its blown into the sky and how high and how are the winds blowing. It's why there's no easy answer, just go with whatever works.
Sounds fair enough. I'll reduce the scale of the nuclear conflict, but otherwise seems like I was on the right track. Also, I know that allies of the US and USSR had nukes too, but I meant like, if they just indiscriminately handed them out. I mean, I think they exercised a bit more caution than that in history... :V
Those sell-by-dates won't stop me because I can't read!

Now, I know what you're thinking; 'nuclear apocalypses are so overdone; ecological collapse is where it's really at'. This is true, however, here I'm talking about an alien planet so it doesn't count. :V
Jokes aside, while developing one of my alien races - of which I have more than I probably should - I started thinking about their history. They're a very militaristic race that has fought with itself a lot over the course of their history, and I figured it'd be a neat twist if the current One Planet Order standard for sci-fi civilization was able to take over solely because it survived a big nuclear war that pretty much wiped out all of its competitors (and for my purposes it doesn't matter if this took place a decade ago or a century ago, that it could happen at all is the key thing. :V)
What I want to know exactly about this scenario is - first of all, assuming this particular nation was ready for a global nuclear war (and this wasn't a Cold War scenario with one major nuclear power attacking another major nuclear power, this was basically every nation on the planet launching nukes at everyone else - think if, say, the US and Soviet Union decided to sell nuclear bombs to all of its allies after WWII, oblivious to the possibility that they might be able to reverse-engineer them and make more), what would they need to do to preserve most of its vital infrastructure? One possible idea I had was that this particular nation was basically a backwater relying mostly on steam power or some other obsolete technology, which meant that their infrastructure was largely unaffected beyond the physical damage caused by the bombs themselves, while more advanced nations had their electronics all wiped out by EMPs.
Second, because I was also thinking about how this would affect the planet's climate (this has nothing to do with the thread's title, I know) - how long is a hypothetical 'Nuclear Winter' supposed to last? I know that Nuclear Winters are supposed to be caused by sunlight being blocked out by radioactive soot in the stratosphere, but I can't find much saying how long this would last for. I kept thinking it'd turn much of the planet into a frozen ocean (since this planet has more ocean than Earth) but knowing my luck I'm probably wrong. :V
Edited by PresidentStalkeyes on Feb 22nd 2020 at 4:47:06 PM
Those sell-by-dates won't stop me because I can't read!