Threads is a population 40 years after nuclear war. It's a more realistic take, and assumes that some parts of the world were more or less spared. The British public was reduced to a medieval level, but other parts of the world have most assuredly survived and thrived.
40 years on, I'd assume there's a neo-colonial movement to occupy the devastated regions and extract labor from the people still living there. That would be The USA, Britain, most of Europe, and western Russia and the majority of the Soviet Union.
On breaching the portal we'd most likely encounter a defensive burgeoning naval power, potentially just a vassal of Australia. New Zealand is a pretty self sufficient place.
I am legend portrays the Darkseekers as intelligent, if inhuman. I can't see them becoming a nation state, but I'd expect them to be tool using tribals living in the ruins 17 years on. The book is much more blatant, but that's not what we're working from. There's no telling how other parts of the world reacted, but the movie suggests that the retrovirus is airborne, but dies rapidly in or near freezing temperatures.
Terminator is too unstable to make any blanket statements about. 2024 might be a year before SkyNet, or it might have already destroyed the resistance and forced the resistance to use time travel. It seems like SkyNet or a replacement is doomed to occur, with every iteration and use of time travel pushing it back a few more years. If that's an abstraction of the Alignment or Super-Alignment problem, they'll probably solve it at some point. One iteration must eventually be the last, either because it solves the problem, or pushes the failure point back far enough for native people to solve it.
That means that Cairo will have either a political issue, or a military issue in defending their new border. If we assume SkyNet is working under the Plague rules, then it's likely fine long term. If not, we'll need to ramp up our cybersecurity to keep SkyNet out of our systems.
The Stand introduces Dark Tower metaphysics which is a mess that I don't feel like addressing right now. Plus it's nearly 50 years on from the plague, and the plague isn't getting to cross over. Likely medieval, with the potential for some Low-Mid fantasy stuff depending on Shine nonsense.
I'm tired poke this if you want more.