They were watching
Independence Day at my place this morning. A truly brainless film that runs on its perverse charm. I never saw the sequel, which my sister, a big fan of the first film, found charmless and dull. Moreover, a rematch strikes me as dull but try this idea...
The aliens struck ten years ago back in the 2040s. The scientists that survived said they were technologically retrograde. To me, that is further proof the aliens were as dumb as a sack of hammers. They're dead, they never seem to have read H.G.Wells or studied bacteriology. The creeps did wipe out the Earth's cities and most of the people. Still, more survives than you'd think.
Basically, a society in transition from TL8 to TL9 gets nearly wiped out by the degenerate remnants of an alien fleet, The shattered remnants are trying to put the world back together.
The aliens seem to have seen China as the center of Earth civilization. So the alien attack hit there first and hardest. Europe, as the second most urbanized area on Earth, was also brutalized. The USA, although hit hard, was less totally torn up than either of the first two areas. Also, a decade and a half of trying to revitalize rural areas meant the USA's infrastructure was far less centralized than most other industrial nations.
Fun wild card. The aliens seem to have been telepathic. Many victims of their telepathic attacks seem to have gained a crude control of psi powers they never knew they had. Thanks to TL9 brain mapping techniques humanity is now beginning to awaken their mental powers.
The PCs could have many roles. Aid workers rebuilding...well anything. PCs as law enforcement agents or soldiers trying to keep the peace or protect those rebuilding society would work too. Diplomatic games either between or within nations seems like a viable option too.