Last week I ruminated pointlessly about good names for fictional planets and/or countries, as opposed to the lame ones we've all come across from time to time ("The United Federal People's Democratic Republic of Arcticstan," etc). That got me to thinking of another SF convention that's kinda' odd.
When you look at habitable planets in SF, the planet is almost always treated like an isolated island nation here on earth: One planet, one government, no clear border excepting space itself, one culture, one language, one monetary system (Assuming they have money), etc. While there might be a specific reason to do this (Planet of clones, or a very small population living entirely in one area, or a hive mind) in general it's simply a case of sloppy-assed writing. Indeed, we tend to see this kind of thing most commonly on TV shows like Trek and Stargate and Doctor Who: Introduce your planet of the week, say that the locals are a "Race of Warriors" or "A race of poets" or "A race of warrior poets" or "A race of hot warrior-poet tabledancers" or something else equally goofy and unreasonably monolithic, and then you move on to your next planet-of-the-week.
TV and Movies are by no means the *ONLY* ones to do this. SF is, on the whole, a genre with a long and frequently badly written history, full of poorly-thought-out stories where unsold cowboy novels are hurriedly re-written to make the cowboy an astronaut, and the indians into aliens, and the Arizona Territory into planet Arizonulon IV. So plenty of room for lazy-assed writing there.
SO why is this bad?
Well, I'm not convinced that it is, it's just sort of a lazy convention, and as with all conventions you need to take 'em out now and again and ask "Why are we doing this again?"
If you think about it rationally, planets are more likely to be something like Continents than Islands. Take the New World here on earth: North and South America were quickly gobbled up by various Old World powers: Spain, Portugal, France, England, The Netherlands, Russia and others. They imposed fairly random borders, and competed with each other. Why? Because everybody wanted a new piece of this huge new pie. They competed, sometimes peacefully, sometimes not, there were winners (England, Spain), losers (Russia, The Netherlands, Sweeden), and some that in the end just kinda broke even (Portugal, France). Yes, granted, there's Australia, which is a continent/colony unto itself, but clearly that's an exception.
And why limit ourselves to the New World? Asia and Africa were similarly divied up between imperial powers. The US even had a piece of that action for a little while.
So what does this have to do with planets?
Well, rather than have Mars be one big happy international colony, it seems more likely to me that you'd have several competing colonies: An American one, A Russian one, a Chinese one, all rather large, and then a half dozen or a dozen smaller ones scattered about - France, Ukraine, Israel, Japan, India, that kind of thing. Given our past history with colonization, this would seem likely.
Or let's assume we've discovered a habitable world orbiting Alpha Centauri. Obviously that'd be quite the prize. Sure, finders keepers, but we all saw how well that worked out for Spain: Whoever gets there and can make a claim stick is gonna' have a piece of it. And everone *WILL* want a piece of it, since a livable world is clearly worth 30 lifeless rocks. So you'll have the "New America" continent and the "New Russia" continent and the "New France Islands" and so on.
Likewise, if we're dealing with aliens, there's no particular reason to assume that aliens will be mushy headed 1960s hippies who want a one-world government. Based on the one example of sapient life we know of (us) and of biology and evolution, it seems that a degree of tribalism and competition is inherent in biology - one wolf pack will fight another for food - apes can and do fight over territory - so an alien world may well have several dozen nations on it as well.
Just something to think about. Why? Because we *don't* tend to think about it. Most people who write SF these days borrow conventions from TV shows thinking there's no other option, but of course there always is, especially when the convention you're copying was only there to save exposition time in a 44-minute adventure show.
It's worth noting that Stanley Weinbaum actually did postulate planets and moons sliced up into colonies by different powers on earth, as does the "Space: 1889" RPG (Remember that one?) and Ursula K. Leguin's slightly-icky novel "The Left Hand of Darkness" revolves around a planet called "Gethen" which is divided up into several well-defined nations. While Niven's "Known Space" stories take place after a one-world government is in place, there are hints that the Moon was divided into national colonies at one point in the past (One city is called "Outer Soviet," for example. I find the "Gethen" example particularly interesting because (If you've read the book) there is absolutely no reason for the planet to be divided up into nations as the people are uniquely homogeneous. They're just kinda' jerks who *like* to do that sort of thing. Just like us. In LeGuin's much less creepy novel, "The Disposessed," she plays it both ways: We see a planet that's divided up into scads of countries, and the planet's habitable Mars-sized moon, which is populated by a small number of hippies (No, really) who have an almost-nonexistent one world government.
So think about it: Are planets Islands or Continents? Well, the ultimate decision rests with what your story needs, but "Continent" is always going to be the more likely and interesting option.