There is a genre called science fiction. I think you would enjoy it.
One aspect of FTL (or even close to light speed) travel is that time would pass at a different rate for travelers than for those on planets. A voyage that takes a year for travelers might find that decades have passed for those at their destination. In one of Ursula K. LeGuin's novels (The Left Hand of Darkness, if I remember correctly), when Earth diplomats would hit a dead end, they would travel part of the way back home and then turn around. By the time they got back to the other planet, years would have passed, and the political situation would have changed. Some books of Orson Scott Card's Ender series make reference to time dilation. And many other books too.
I'm assuming that voyages only take the space of several days, or hours, even to an outside observer, so even though time dilation occurs, it wouldn't have an incredible effect unless you're someone who spends a great time FTL. This may not be plausible, but unless spaceships could get from planet to planet speedily, there would be no real reason for ties between colonies and governing planets.
Are we assuming communication as improved to outpace travel speed? That might affect interplanetary diplomacy.
I imagine "first world" would take on a new meaning, as a name for a completely unified planet.
What about intelligent aliens, too?
as far as communication outpacing lightspeed, I think that wouldn't be plausible, and, if we assume that basically any FTL transit (on a spaceship) can be done in less than a day, or several days, it would be unneeded, as ships could carry communications. As far as intelligent aliens, I believe it would be impossible to guess how they would act, so while you're welcome to speculate about them, I'm going to pretend they don't exist.
As to "first worlds" while I believe earth, with its religious and historical connotations, as well as the earliest planets we colonized (while still traveling below light speed in generation ships and the like), would still be split up between various nations, but after that, most worlds would be controlled by one nation- it would originally be easier to find a new planet and colonize it than to take over another planet from someone else.
