Yes, TO PLANETS. The easiest way to do that is to park your ships in the vicinity of a planet you want to control and don't let anyone else near it.
But you can't park them there if fifty lightyears of enemy territory sit between your ships and that planet.
Are you postulating that every planet ought to have its own defense fleet that never leaves said planet? This might be how "real" star empires work, but Trek and its warp drive make the idea untenable. If you split your ships in penny packets around specific planets (each of which has to manufacture its own ships, what with being bottled up by the enemy holdings), the enemy can concentrate its forces at will and gobble up each penny packet without resistance.
Trek features effortless movement from star system to star system. This absolutely requires the formal control of access, and conversely the challenging of said control.
Otherwise, you're just watching the other guy's ships go screaming past you at warp speed and shaking your fists at them as they pass you by, which is pretty much what I mean by "unenforceable."
Why wouldn't you shoot them down instead? Anybody and his Pakled cousin can do warp chases and force the escaping party out of warp for comeuppance.
The trick is only in meeting the enemy in the vastness of space (meaning "border defenses" are like minefields - a certain
very low statistical chance of getting intercepted is coupled with severe repercussions). But when you do, you want the formal right to declare the trespasser dead. You certainy don't want to give yp that right for nothing.
Same reason why the various countries of the world have not yet claimed every square inch of ocean in the world today. "International waters" are a thing for a reason.
Not really. They used to be, back when oceans could be controlled, and they are sort of grandfathered in. But grandpatricide poses no problems, thus e.g. China can claim all the waters it wishes, as long as somebody else doesn't get there first, and with bigger guns.
Leaving empty space unclaimed in Trek would be as absurd as Russia deciding that all those thousands of worthless square miles of Siberia between the worthwhile oil wells can be ceded to Germany or Lichtenstein, whichever claims them first.
Routes do not need defending. CARGO needs defending. Your ability to prevent cargo from reaching its destination defines your control of the region through which that cargo travels.
So if A sets up a pirate fleet, B can do nothing about it stalking out there, because it's out of their jurisdiction?
The same factors that make it difficult to intercept also make it near-impossible to defend the shipments, unless one enjoys the right to blow to smithereens the pirates whenever they are met, not merely when they can be shown to be engaging in piracy. And there is no difference between a "shoot first, fine the next-of-kind later" and a territorial claim.
That means a permanent military presence, ships, space stations, colonies and outposts.
No, that's the losing strategy. Strategic mobility is the key: your fleets must be able to be concentrated against the threat, meaning they have no business being at any specific spot at any specific time, least of all where the enemy expects them to be.
To control a vast ocean, you declare it yours, and if you spot somebody's frigate there, your entire fleet goes to flatten six of his cities (with nukes or 14 inch shells, depending on the era) and tells him not to do it again. That's how you find wars in the plains, that's how you would fight wars on the oceans if not for certain grandfather clauses and the unfortunate fact that oceans are so darn small and the ports to close to each other that the reprisals are a tad too easy to conduct.
"Just to spite the other guy" is not a coherent military goal, and it certainly isn't something you'd commit your entire fleet to. Unless you're being governed by imbeciles, which I admit is a distinct political possibility.
Well, spiting is what real fleets do about 99% of their time, in pretty much every era outside open war. Having a military of any sort is all about posturing, first and foremost.
You can draw the lines anywhere you damn well please, the point is EVERYONE ELSE will draw them somewhere else.
And then the strongest one wins. But if you don't draw any lines, you automatically lose, and every one of your planets is subject to siege you can do nothing about.
The reason governments don't make bullshit claims like that is because it is political suicide for a country to deliberately demonstrate its own weakness.
There is no country today that would either refrain from making bullshit claims about its borders, or be able to defend said countries if somebody really put his heart into it. But nobody usually does, exactly because everybody else can retaliate. This has not led to
any bullshit border failing to get drawn on the map so far.
Measure it FROM WHAT? The vacuum of space is, by definition, devoid of landmarks. The only way to even know you're IN that region of space is by judging the distance between the nearby stars, which in the mean time are constantly in motion relative to one another.
So you claim that Trek ships can't navigate? That's a non-starter - everybody in Trek knows well enough where everything else is. This isn't the 17th century any more - don't try and invent objections that aren't merely outside the scope of Trek but anachronistic to begin with.
It would be like Germany trying to claim the entire Atlantic Ocean just to keep the allies from sending supplies to Great Brittain.
Which is exactly what they did, in two world wars. As said, there's no difference between "anything that moves within our territory is dead if we happen upon it" and "this territory is ours".
Timo Saloniemi