If human history suggests anything, it would be that at a certain point invading other colonies will become more profitable than founding new colonies in sub-optimal locations.

Invading another star system of similar technology levels without FTL seems like non starter. You could sterilize planets, but space based assets are another story and retribution is possible.

Yes. Invading ships wouldn't be able to bring a lot of fuel/propellant with them beyond what's necessary to decelerate from the trip. And they would have to be warm enough to support life, so they'd radiate a lot of heat. They'd be easy to spot. So no fancy maneuvering and no stealth. And the defenders have the resources of an entire star system to throw at you.

Terrorism, as you mention, might be possible (but again remember, no stealth) and claim jumping (where you displace another group that got there roughly when you did). But even in densely packed stellar neighborhoods the average star is surrounded by a moat several light years across. Once the locals are developed enough to mount a serious defense, they're probably immovable.

Invaders might not need to bring anything with them at all. Particularly relevant to your point, I'll share one of the military projects from Sid Meier's Alpha Centauri: https://www.youtube.com/watch?v=aKcEwUcVBHs

More generally, the point I'm raising is symbolized in entirety by the Spartan faction's ideology in that narrative environment.

You still lose to the first-mover advantage though. If universal assemblers are possible, then the defender with the resources of a star system at their disposal and early warning of the attack is going to outproduce the aggressor.

The only advantage I imagine an invader would possess is the possibility of taking control of the Lagrange points and any orbital production facilities, and then besieging the population below.

Dropping asteroids on habitable worlds and causing ice ages to clear out the population _might_ still be faster/cheaper than terraforming a semi-hostile world.

That assumes the Lagrange points are empty. A civilization capable of interstellar war is going to have a lot of space based assets.

Further starship drive capable of reaching a significant fraction of the speed of light make one hell of a weapon. But you still need to deal with space based assets that can dodge your initial bombardment and at a minimum are armed with powerful engines. So sure you can destroy planetary populations etc, but now your still out gunned 1,000:1 locally and pissed off a civilization capable of doing the same thing to you. Net result MAD.

A large technical advantage may make up for this, but that means the winner has better tech is much harder to take over a second time. On top of this the only thing worth shipping between stars is information at the speed of light. Making conquest largely pointless without FTL.

> On top of this the only thing worth shipping between stars is information at the speed of light.

It could be worthwhile to beam energy out to interstellar distances (also at the speed of light). This is probably needed for interstellar travel anyway.

Eh? Physical war is almost obsolete today.

> The only thing that needs to be preserved is the desire to build more colonies

That's hard. I'd say harder than solving the physical problems of interstellar travel. Once a generation has learned to live with the limited resources of a starship, living with the limited resources of a planet is going to be a very attractive option. What's their incentive to colonize more from there?

In the long run resource shortage goes down. Technology increases the amount of output possible for a given amount of effort over a given amount of matter. For example: wood to coal to oil to nuclear. Thinking about starships of 3000 AD we're talking about a thousand years of scientific development towards nuclear reactors, food processing, scientific computing, and random technologies I can't even fathom because they'll rest on a bed of mathematics and physics that's not even conceivable yet.

If more technologically advanced aliens exist then our not sensing them is much more likely because they don't want to be sensed than some other consideration like them stopping to setup on some habitable planet. I'm horrified about war, and I'd hope they would be too, but it may be that aliens come to understand species or ecosystems in a more expansive way and may consider the process of ending war as a necessary one for the maturation of an ecosystem.

Or the great filter is true. We all end up killing ourselves because it's impossible to escape exponential technology growth and mismatched incentive problems, or something else like that.

It's always going to be a small percentage that desires to venture further out to new areas. On a newly settled planet, most will not want to leave. But some will.

But you have to wait for that society to forget that living on a starship means spending your whole life never venturing out, while a planet lets you spend your life exploring.

Or, you know, some just want to get away from the other individuals.

That is, if we are talking about something comparable to current humans. Immortal super AIs might don't care about idling in the void for a few million years, just for the opportunity to re-sync those gained experiences to their decentralized knowledge a few million years down the line. I really like the single omnipotent AI scenario, since being immortal and not depending on others changes quite drastically what strategies can be successful - it won't be anything like human kings who need to keep their subjects at bay and working for them to support their power and limited life. But we shouldn't restrict our imagination, if we are talking about possibilities and galactic time-spans.

The important part is, as mentioned by GP, the desire to expand, since this is a dominant strategy. In comparison, not every living being on earth has the drive to participate in evolution by e.g. creating offspring. Those usually just drop out of the "game" and likely won't matter in the long term, at worst making it a bit harder for the others initially till their disappearance. What matters are those who have persistent impact... e.g. by colonizing/making offspring.

And that doesn't need to happen with anywhere near 100% accuracy. If 1% of the offspring multiplies and works to found new colonies that barely changes the dynamics or speed of spreading.

Even on earth we had plenty of colonies rebelling against the founding nation, gaining independence and becoming a serious competitor. Britain might conclude that they would be better off today had they never colonized America and India. Repeat this pattern often enough over millennia and it seems plausible that an entire race might become very cautious with forming permanent colonies.

Britain had to colonize the Americas or France and Spain would have without them. It would take another 200 years for the empire to fully collapse. It’s hard to say colonization was a net negative just because of America’s independence.

Further it seems much less likely the populace would be so willing to send aide to Britain during WWI if it weren’t for the cultural similarities. If instead Spain had colonized the US it seems very likely the country would have remained neutral as Spain did.

My gut feeling would say colonization was a net positive to Britain, but it's hard to say. It's just too big of a what-if. The US would have likely gone to France, their main rival at the time. On the other hand Britain spend a lot of resources on their US colonies, both building them and fighting France in America. Who knows what else they could have with those resources.

It's not just the US either. India was a profitable colony at the time but might turn out to be a major detriment to Britain overall, both as a source of cheap skilled labor and as a powerful nation of their own. Who knows what would have happened without the British. A lot of the borders in the Middle East are drawn by Britain as part of their WWI mandates/colonies, and the problems from how those borders were drawn spill over into Britain (yes, it's not the only problem in the Middle East by a long shot, but it's one of them).

I still think overall Britain came out ahead (just look at Hong Kong for what cultural influence can do), but it's not hard to imagine how colonization might be seen as a net negative if a few times things turned out even slightly worse.

Spain did colonise much of what is now the USA. That’s why it’s “Los Angeles” and “San Francisco”.

https://commons.m.wikimedia.org/wiki/File:Imperios_Español_y...

And Louisiana was French.

Britain seeded the Earth with English speakers that inherited her legal traditions and cultural values for the most part that then developed into rich trading partners that participate in an international system of voluntary exchange that has enriched the British.

It could have gone another way, there’s a reason we’re talking about Britain instead of England and Scotland, but I would say it has worked out brilliantly.

Not just the desire, but also the ability- the cultural context for an industrial base potentially far more powerful than what we have. That may be extremely difficult to sustain over such timescales.