I do like the Star Trek model, now that you mention it. Earth as one unified nation, no more wars, tribalism, racism etc.
If and when mankind emigrates to Mars or other habitable planet, that will be an interesting situation. Will the people on Earth unite against the people on Mars? Or will Mars become a united nation? Who will move there and who won't?
Heh, well, if you've ever read the Red Dwarf novels you might be familiar with a concept from The Last Human. It tells a little story about what happened some years after the Red Dwarf was lost and what became of earth between Lister having left it and his search to find it again 3,000,000 years later.
In Red Dwarf we're made familiar with the concept that the solar system is fully inhabited. Rimmer himself comes from Io, one of Jupiter's moons, and has never set foot on Earth. Essentially, in the book it tells of how the abject waste of human consumerism was filling the solar system with junk. All planets and moons took a vote on which of them was least popular and so to be turned into a giant dump. Unsurprisingly, Earth got the vote and so was evaccuated and turned into a giant garbage planet.
That's triabalism and democracy in action
