Overworld was a setting for my SA RPG Beta Test. It is an example of how societies can change, especially when in contact with one another.
Overworld was once a Cargo Cult, but is now better classified as Old Worlder. Its name derives from its later belief that below the ground is the hellish inferno of underworld.
The fabrication factories of Overworld were extremely powerful, but the people forgot how to ask them to make their own fuel. The best they could to was create mechanisms which, when subjected to extreme heat, would power the factories. So, the people ran their nuclear power plants and prospered… until they ran out of fissionable material. Then, the fragmenting nations began to burn the planet's fossil fuels, until they too were exhausted. The people began to see the factories as demons incarnate. Powerful, but greedy and fundamentally evil. Finally, the warring clans, desperate to feed the demonic machines to which they owed their power, fed them the very trees as sacrifice. In the end, when there was nothing left to burn, the old fabricators, under their dark alters of bones, fell silent. The sky had become black with the smoke of the sacrificial fires. The rain burned the flesh, and the seas were death. And so the people of Overworld clung to the little life they had left, occasionally scraping enough burnable material to make another offering to a hidden demon, for some temporary protection against the horrors.
Then, two generations after the final fall, the Tao of History arrived. The Tao made a deal with the myriad clans. In return for a single continent to use for their own ends, the Tao would repair the destroyed environment, and return life to Overworld. The clans agreed, and so the slow repair of Overworld began. The old demon cults died, and the factories were shunned and left to decay in the new forests. Many Overworlders, in awe of the Tao's power, chose to join them and the other civilizations. Those who chose to stay behind shunned technology and became old worlders.