Try this one...
The Coalition Space Fleet Scouting ship made a discovery in the new sector they were in no way prepared for...the
United States of America! They were mildly confused to say the least.
Once they had a chance to understand the story offered by the "Americans," they reported that it appeared that some ninety-five years earlier (by the old calendar 2847 CE) a large section of the planet Earth was duplicated. This section contained all of the North American continent from
Jalisco north, all the inhabited islands of the Caribbean, and all the inhabited islands of
Polynesia including New Zealand. To the locals the event happened in late September 1941. During the event the locals that experienced it were told they were being moved into deep space as was everyone else on Earth to save humanity. And that they would have the duty of getting into space and finding everyone else.
The planet the North Americans, Polynesians, New Zealanders, and Caribbean Islanders found themselves on was basically Earthlike. The gavity was just noticeably less that Earth normal (0.94 G). The day was only three minuets longer. The geography of the planet beyond the duplicated areas was wildly unearthlike although all the lifeforms on the planet seemed to be Earth animals and plants, many long extinct on Earth. Animals from
Andrewsarchus to
Chalicotheres to
Quagga keep showing up and causing confusion or worse.
By what the locals consider to be the year 2036 this Earth is TL8 across the board and advanced in space travel and material science. No threat to a TL12^ society like the Coalition but possibly a new ally or member. Since the discovery of New America,other worlds with past cultures placed on them have been found. Ming China, Imperial Rome, the pre-Roman conquest Celts, three separate African Empires, 17th century Europe with Russia to the Urals, the Caribbean, and North America to the Alleghenies, the Islamic Empires from Spain to the
Fergana Valley, and many other culturally rich and lively slices of Earth history. All of these worlds believe they were transferred to their "New World" at roughly the same time as the first world they discovered.
This setting has two major themes/possibilities. First crossover games, your space heroes can deal with all sorts of alternative histories. Second, finding out who created these New Earths and why.