One of the longest running campaigns I’ve ever run was a Gamma World game based on the original first edition rules. In building the world, I used not only elements from the setting sketched out in the book, but elements from other game settings like The Morrow Project and Aftermath along with ideas from film and fiction. The most direct lift was the territory controlled by the Eleveners, a direct lift from Hiero’s Journey by Sterling E. Lanier and its sequel, though the actual details of their society included elements from Miller’s A Canticle for Liebowitz and was a combination of Healers and Restorationists as presented as Cryptic Alliances in the setting. Lifewise, the Brotherhood of the Unclean became simply The Unclean as the dark side to the Restorationists with a healthy dose of other antagonists thrown in including, most predominantly, Radioactivists.
Apart from these two antagonistic organizations, the campaign started in the confederation known as the Northern League with territory nominally claimed by the city-states there. I drew on Aftermath’s Operation Morpheus with a more high-tech bent where the cryogenically-frozen “Sleepers” were part of a government program, having more of a flavor of the Morrow Project. Without providing the players with power armor and too much technology right out of the gate, I wanted something that had more science fiction than the modern Cold War tech of other extant post-holocaust games that influenced me, while preserving the things that made them and other rule systems like Twilight 2000 so dangerous. As a result, the relations between the groups became increasingly important and the role of the players was as much diplomatic as anything, requiring them to enlist the North League’s natural allies, the Eleveners, in a fight against the Unclean by resolving the conflicts with the nomadic tribes known as the Death Groups on their eastern border.
As the campaign progressed, other groups entered the story. The players travelled further south and further to the east. A fellow gamemaster developed the area to the north and ran some adventures in that part of the world.As the Unclean were driven back, the campaign entered a new phase with a new and greater threat rising in the east. Influenced equally by the later Gamma World adventures that came from TSR (since I found the earlier adventures uninspiring and a poor fit for my gamemastering style) and Saberhagen’s Empire of the East (particularly the third part of that omnibus novel, Changeling Earth, also known as Ardneh’s World). The new threat led, in turn, to new groups like the Immortals whose knowledge of the old times made them a match for the surviving Sleepers. I’m pretty sure the ideas about their structures and infiltration of groups already familiar to the players preceded Marvel’s introduction of the Externals, but they may have been influenced by a subconscious recollection of episodes of Thundarr the Barbarian (Mindok the Mind Menace, perhaps?). Their existence led to the addition of hidden outposts, ancient bases, and other places whose existence the players had previously been unaware of. As a result, the game maps became ever smaller and more detailed.