The sourcebook Howling Wilderness sets the basis for the remaining North American setting in Twilight 2000.
I feel that in an isolated spherical cow world, the North American modules of Twilight 2000 should have been a different setting, something like “Apocalypse 2000”. It would probably be a good idea to alter the rules so that the out-there adventures can be a lot more viable. But theme alone would be enough to make the switch.
There’s two literary problems with actually keeping it and the original European setting part of the same universe. The first is the creative regression. The European setting is a clever way to square the circle of “Ok, we want you to be in the army but we also want you to be able to run free. We’ll make this post-apocalyptic, but not too post-apocalyptic, since we still want there to be tons of those tanks around.” There are still flaws, and not just the impossibility to balance dark struggles for survival, rivet-counting crunchy gaming, and traditional RPG adventure that all appear in the rules.
Enter this, where the setting is more of a traditional post-apocalyptic one. North America has been crushed by a mega-drought and everyone has withered down. This leads to the second problem, which is how this led to gimmicks. It feels like the setting should be doubling down on the “grim survival” element, but then an individual sourcebook has a submarine plot right out of Jerry Ahern’s Survivalist, making things more muddled than ever.
I don’t blame GDW for releasing new content out of business necessity. I also think that, given the flexibility GMs have for actually running games, the negative effects of any official supplement are inherently limited. But I still feel that, like how the Survivalist jumped the shark post-timeskip, Twilight 2000 also jumped post Atlantic crossing.