Namely, the history of the space opera I'm trying to set up. Plot requires that a modern-ish level of technology Earth is faced with an extinction level event, and hollow out a few asteroids to get the hell out of there (no, the rest of the solar system isn't safe either. Or is too safe, depending on your point of view.) They travel to a nearby system, terraform a planet, move in, and then some set off towards another so that their eggs aren't all in one basket. However, at the same time, a few pockets of 'lucky' survivors on Earth are desperately trying to get out of there as well, having developed FTL travel as a result of the extinction level event.
The problem is, any timescale that's remotely realistic for sub-light edenship travel means those stuck on Earth should have a much greater population than is really possible for storline purposes. Even if I set the nearest habitable planet five light years away, giving five thousand years for travel seems awfully fast, (although
this guy calculates that with 21 gigatons of fuel, they could get 25 gigatons of spacehip to Epsilon Eridani in under 750 years). My edenships can't have Orion propulsion for plot reasons, either, so they're stuck with Bussard's ramjets and fusion candles.
The problem is, how do I get them to the new planet and away (terraforming has a plot reason for going much faster than you might expect) without those left behind having enough thme to get into space, build a lot of space colonies and grow to a large enough number that it's difficult to get them out of there once FTL travel comes along. The Earth system is supposed to end up as a dead backwater, just a few miners in the asteriods, while the political, economic and social centres are elsewhere. It's hard to see Earth losing power unless there's both somewhere else for everybody to go, and enough spaceships to get everyone there - something Asimov's later stories have done.
The main solution I can think of is two stage - first, fudge the timeline by never stating it exactly. Second, details of governments during the extinction event and the subsequent expansion - since by definition, the genetic diversity of the surviving population will be much lower, in order to prevent massive inbreeding, there has to be some form of organisation that will assign parenthoods. Coupled with the small bunkers / space stations that a required for survival on an iceball Earth and cannot withstand inhabitants fighting amongst themselves, it seems inevitable that you'll end up with either a totalitarian government where a small ruling group chuck out any dissenters or a totalitarian government where a small ruling group pretend to be doing the will of everybody. That kind of government, based around preserving the status quo would still undergo upheaval every time there's a new ruler, and some would be expansionist, but since they'd want to keep a very close watch on any new colonies they set up, they'd grow slowly. An emphasis on using resources simply to survive and not having much left over for research etc would help a lot.
I suppose this stuff is all very far in the background of my story - which takes place thousands of years later once the first wave of settled planets are well established, and the second wave are getting on their feet, but there are a lot of tensions from that era that keep coming up - ancient prejudices and hatreds that won't go away, so I want to be clear in my head what happened.
I also want to be clear in my head without this damn cold! It feels like I've been punched inside my throat.