Here is the setup for my group's next adventure in the Alpha Playtest:
Demarcadia is a large moon of a Jovian sized gas giant fairly close in to the primary. It very Earth-like, wet and lush with vegetation, with a singularly productive soil and good deposits of ore. It is tidally locked to the Gas Giant, but as the Jovian planet is itself in orbit about the primary, there is no un-uniform heating. It was and is a perfect planet for humans to settle.
It was slated to be a target for the slow boat Prometheus in the initial wave of settlement from Earth. When first contacted by outsiders, a couple hundred years later, there were no humans on the planet, but there were a half-dozen different animals who had been uplifted into several dozen species. They spoke an English-derived language, like the humans on the Prometheus, who practiced Early 20th century American cultural emulation, but the technology level necessary to uplift these species had not been maintained one the humans were gone. The animals had managed to maintain a steam-based technology (Tech Level 5) in one area of the main continetal mass.
When asked what happened to the humans, the animals shrugged and said that they died out after producing their various species. They did not permit archaeological digs to verify this, and did not go into detail as to exactly how the humans all happened to die. It is assumed that the human culture mistreated the uplifts, and they rose in rebellion, slaughtering the humans to a man. They remain skittish of humans to this day, limiting contact severely.
In the last three hundred years, the uplifts have developed and sustained a Tech Level 6 (Internal Combustion) culture of 2.5 billion, which has spread uniformly over the entire moon. There is a planet-wide semi-government with limited powers which maintains Affiliate status with the SaVaHuTa league, with representation based on the parent species (Chords) which is subdivided into representation based on uplift species (Strings), several of which are typically derived from the same parent species. There are no territorial nations, Chords and Stringe taking that niche in the culture. The various uplift species are therefore very intermixed.
There have been wars, both inter-Chord and extra-Chord, in the recent past. Philosphy, politics, and religion are all possible flash points which may touch one off. Very recently, requests for help were recieved from Demarcadia asking for help with an epidemic which seemed to be spreading. Several volunteer groups have responded, sending in teams of specialists to help out.