Minimum invasion force level

[speaker-to-trolls]

Any society advanced enough to travel to earth in the first place can conqueror us. Earth getting uppity? Drop a few rocks on our head. They can redirect comets or simply attach a few engines on one of the bigger rocks in the Asteroid belt and aim it our way.

(FYI there are over 220 "Planet killer" sized rocks in the Asteroid belt, IE objects 100km's or larger) Any one of which impacting anywhere on the earth would cause a 12 Richter scale earthquake in that area and a five hundred plus kilometer crater, oh and toss enough dust into the atmosphere to kill all plant life. So if it say hit Britian it of course takes out London and ever Berlin is being hit with an nice large earthquake.

And they have over two hundred to chose from. Attach engines to them then plotting courses so they hit the Earth at comet sized speeds(51+ Kps) is not that hard since they can use the Earth's orbit against us(That's a free +28 Kps right there) and angle the orbit so it goes counter-clockwise to us and impact at a place of their chosing.

An object that size and being intelligently guided? No way we can stop it. And all it takes is a space-fairing race with a spare engine or hell some tow cables. It might burn up the reactor mass but they can tow the rock into place themselves if they like.

No need for nano-techology, no need for death rays, power armor, super virus or anything else. Play nice or eat rock Earth.

I think a 100km rock is overkill, wasn't the KT boundary asteroid something like 10km? Another one like that would pretty well ruin our day, and our next 3 million days after that.

I don't think they'd resort to this if they want our ecosystem and/or civilisation intact, but then the question, as many others have pointed out, is how intact are they prepared to take it? Our situation is still pretty damn grim if they're prepared to flatten our major cities with smaller asteroids (the size an asteroid needs to be to produce a nuclear level explosion is scarily small) or torpedoes or whatever.

BUT, then we get to the problem of occupying an entire planet. And this is where our hypothetical overlords might benefit from cultivating the support of the locals. If they want anything from us they will have to come down here to get it, whether it's living space or resources that they're after (we certainly can't get anything up to them in bulk), and then they will have to deal with us on more even terms, and I don't think resorting to "do as we say or we blow up one of the six remaining major cities" is going to be a very practical tactic if they use it to often. If nothing else they'll probably run out of cities.

Of course, they are aliens and we know nothing about their motivations, but my guess would be if they pursue conquest in anything like the same way we do, then they'll probably start by setting up a kind of Hispaniola on the moon, in orbit or somewhere secluded on Earth and start recruiting allies. They'd probably select someone with a grudge against the biggest power and then help them displace them, hard luck America, but whether they'd choose a big player like Russia/China/India or a relatively minor nation or group of nations I couldn't say. But remember they can choose whoever they want, if they sign an alliance with Iran then Iran becomes inviolate. You just try to bomb their nuclear facilities when their friends can shoot your planes out of the air with lasers, and that's if your planes get past the swarm of atmospheric fighter drones.

[The Romulan Republic]

If they have no FTL, then they won't be able to send regular reinforcements if things go bad. If I was commanding the invasion force, therefore, I would probably do something like this:

First, send as many people and as much equipment as possible on a multi-generational ship. I'm going to make sure I have more than the minimum, because I can't count on reinforcements. Make sure the expedition is completely self-sufficient.

Next, I would set up a main base on Mars, since it has more resources than the Moon. I would also put a forward command center and space port on the Moon, from which I would launch attacks on Earth.

From their, collaborate with the humans. Use displays of technological prowess, messages of peace, promises of trading advanced technology. Lots of propaganda to sell my forces as benevolent benefactors. Get some local allies, so that ideally I can have a peaceful takeover, and at worst fight by proxy, overcoming my lack of numbers without having to resort to WMDs.

If properly executed this plan would require at most a handful of soldiers to operate the equipment and ships, plus perhaps some more to act as ambassadors and guards during negotiations. And that's if I don't just crew everything with AIs. However, being so far from home, I would probably bring along enough people to establish a stable population if possible.

[speaker-to-trolls]

If properly executed this plan would require at most a handful of soldiers to operate the equipment and ships, plus perhaps some more to act as ambassadors and guards during negotiations. And that's if I don't just crew everything with AIs. However, being so far from home, I would probably bring along enough people to establish a stable population if possible.

You shouldn't have to worry about population size, all you need to do is bring along a decent number of frozen embryos and exo-wombs, if these are available.

[Strider]

There are a lot of non-military variable that also need to be factored in that may change the dynamics of the invasion. First off, why are they coming to our Solar System, and what do they want that Earth has that cannot be had anywhere else? Is it possibly something they can get by trade or bargaining? Why have they chosen invasion as their only course of action, since, as a society only 50 years in advance of us, it is inefficient and carries a significant risk factor?

Would it be easier or more efficient for the aliens to show up and find a willing subject nation and use them as proxies? Suck up to the US, Russia, or China by offering us something awesome in exchange for the use of our troops to further their cause?

Any of these things may change how this is carried out.

There is only one commodity that aliens could get on Earth and nowhere else: Information. Coming all the way here for resources is laughably impractical, and coming for living space would be a primitive mindset at best and unbelievable inefficiency at worst. Coming for labor might make a little more sense, but Humans are clever, grudge holding, hateful little buggers, and I wouldn't trust them father than I could throw 'em to do anything sensitive enough that 2008 Earth couldn't build a robot to do. (While a straightforward defense of Terra would be impossible, I find it much easier to see situations where aliens try to enslave humanity and end up dead and conquered 50 years later.)

The only thing we've got in any sort of bulk that can be easily exported and has at least some value is the mind-bogglingly huge torrent of information Earth is constantly spitting out. Sure, very little of it has any *practical* value, but if you're a really bored bunch of aliens, suddenly what makes the most sense is that you wanted to come here to steal our TV shows. How does this change things? Well, RIAA aside, I don't think any major powers or governments are going to fight to the death to keep safe the Hitchhiker's Guide to the Galaxy and Season 3 of Seinfeld, so there is probably little reason for an "invading" group of aliens to bring anything more than enough weapons to keep the Earthers too scared to attack them.

[Samuel]

There are a lot of non-military variable that also need to be factored in that may change the dynamics of the invasion. First off, why are they coming to our Solar System, and what do they want that Earth has that cannot be had anywhere else? Is it possibly something they can get by trade or bargaining? Why have they chosen invasion as their only course of action, since, as a society only 50 years in advance of us, it is inefficient and carries a significant risk factor?

Would it be easier or more efficient for the aliens to show up and find a willing subject nation and use them as proxies? Suck up to the US, Russia, or China by offering us something awesome in exchange for the use of our troops to further their cause?

Any of these things may change how this is carried out.

There is only one commodity that aliens could get on Earth and nowhere else: Information. Coming all the way here for resources is laughably impractical, and coming for living space would be a primitive mindset at best and unbelievable inefficiency at worst. Coming for labor might make a little more sense, but Humans are clever, grudge holding, hateful little buggers, and I wouldn't trust them father than I could throw 'em to do anything sensitive enough that 2008 Earth couldn't build a robot to do. (While a straightforward defense of Terra would be impossible, I find it much easier to see situations where aliens try to enslave humanity and end up dead and conquered 50 years later.)

The only thing we've got in any sort of bulk that can be easily exported and has at least some value is the mind-bogglingly huge torrent of information Earth is constantly spitting out. Sure, very little of it has any *practical* value, but if you're a really bored bunch of aliens, suddenly what makes the most sense is that you wanted to come here to steal our TV shows. How does this change things? Well, RIAA aside, I don't think any major powers or governments are going to fight to the death to keep safe the Hitchhiker's Guide to the Galaxy and Season 3 of Seinfeld, so there is probably little reason for an "invading" group of aliens to bring anything more than enough weapons to keep the Earthers too scared to attack them.

Why bother even invading? Seen a probe to pick up signals and hack into the internet. Problem solved.

[Darth Tanner]

Just demand that we turn over what resources they want or they remove a major city, no landings, no occupation, no real risk to themselves. Just turn up and get what they want before leaving with their cargo holds full. They don't even need to bother developing an industrial base on the planet, we'll do all the work for them. I highly doubt world leaders are going to hesitate to bow down to them after say New York, Cairo and Shanghai are reduced to radioactive dust by whatever passes for ordinance on their ships.

Of course that assumes we can provide what they want. If their bothering with a sub light invasion of a star system and have been travelling for centuries or so to get here then their only really going to be after the one thing of value we have, a planet capable of supporting life. To remove us the best answer would probably be some form of engineered virus, but that would likely take them a long time to develop, as they likely have no experience with our genetics. Of course if they happen to have a cargo hold of antimatter bombs then simply eradicating all human life becomes quite easy, but damage to the ecosystem seems inevitable if they resort to that.

[The Romulan Republic]

There is only one commodity that aliens could get on Earth and nowhere else: Information. Coming all the way here for resources is laughably impractical, and coming for living space would be a primitive mindset at best and unbelievable inefficiency at worst. Coming for labor might make a little more sense, but Humans are clever, grudge holding, hateful little buggers, and I wouldn't trust them father than I could throw 'em to do anything sensitive enough that 2008 Earth couldn't build a robot to do. (While a straightforward defense of Terra would be impossible, I find it much easier to see situations where aliens try to enslave humanity and end up dead and conquered 50 years later.)

Barring very unlikely and exceptional circumstances, there's probably no good reason to attack Earth. You don't need to invade to get information. However, their is religious fanaticism. Never underestimate the power of religion to drive irrational decisions. Extra-terrestrial conquest would almost have to be motivated by religious, xenophobic or nationalistic concepts of imperialism or "manifest destiny". You'd be hard pressed to contrive a practical reason to undertake an interstellar invasion.

[Darth Tanner]

You'd be hard pressed to contrive a practical reason to undertake an interstellar invasion.

Xenophobia does have a practical reason. If they wipe us out now while we are easy prey then there’s no risk of us eventually posing a threat to them in several millennia. If the alien government is sufficiently murderous or simply doesn’t recognise 'lower life forms' as being equal with their own then they could simply be going about murdering any potential threat. Also a simple review of our history would reveal our violent expansionist past.

You don't need to invade to get information.

Are you kidding? With our copyright laws do you think we'd just give up or even trade away so many intellectual rights to some aliens just because they could turn earth into an ash ball!

Coming for labor might make a little more sense

I seriously doubt any society more advanced than the internal combustion engine would still be using slave labour. Unless we're discovered by alien criminals/pirates of course.

[The Romulan Republic]

You'd be hard pressed to contrive a practical reason to undertake an interstellar invasion.

Xenophobia does have a practical reason. If they wipe us out now while we are easy prey then there’s no risk of us eventually posing a threat to them in several millennia. If the alien government is sufficiently murderous or simply doesn’t recognise 'lower life forms' as being equal with their own then they could simply be going about murdering any potential threat. Also a simple review of our history would reveal our violent expansionist past.

On the other hand, you lose any potential gains of maintaining that world intact, and if alien civilizations are common, you run the risk that another interstellar civilization will observe your genocidal behavior and decide to wipe you out.

[Samuel]

Not to mention that if they are ahead of us, there is no reason they would ever loose their lead.

I like "we are here to help" though.

[Strider]

Coming for labor might make a little more sense

I seriously doubt any society more advanced than the internal combustion engine would still be using slave labour. Unless we're discovered by alien criminals/pirates of course.

I was more thinking *intelligent* labor, for various things that alien AI was not smart enough to do. Thus slave revolts become a very real fear, since being used in intelligent labor would inevitably give humans more access to things they can muck up.

Back on the general theme, I guess one completely logical reason for an alien invasion which I overlooked is extermination. Aliens might reasonably fear that if we meet them eventually on equal terms, we will find some stupid reason to start a war and then proceed to wipe them out or hurt them badly. Incidentally, this would be a likely aftermath of a slave revolt in the Sol system: a war of extermination against the alien threat (and possibly whatever other alien threats we encounter).

Interestingly, this means that if logical aliens come knocking, it is very unlikely there would be any sort of ground, or even atmospheric, war. They would either have fairly peaceful intentions or drop rocks or bombs on Earth till it was dead. The intelligent human species would really be a much more important variable to any visitors than some totally alien biosphere at the bottom of an air filled gravity well.

Then again, I guess there's no reason the aliens really need to have logical reasons for doing things, since after all, humans usually don't. In the event of ground War, I'd be betting they were looking for cheap smart labor (and perhaps not fully understanding the risks involved).

[Samuel]

How can a species that has the concept of slave labor not understand the concept of slave revolt? That would require an extremely screwed up psychology.

It also isn't logical to exterminate humanity. If you can only use sublight transit there is no way they can be a problem if you are more advanced than them. Why? Because you have a tech and infrastructure lead that they can never catch up to. So unless your species periodically has horrific wars where you destroy everything (moties, TBO), this wouldn't be a concern.

[Darth Tanner]

Because you have a tech and infrastructure lead that they can never catch up to.

We don't need to catch up to post a threat/problem. Simply by existing we are using resources and space that they could be, and once we do start to colonise other star systems that problem will grow exponentially over the millennia. Also it is possible for one species to catch up technologically with another, especially when they have become exposed to each other’s existence and trade/theft has begun to spread ideas, and that’s ignoring the idea of a technological plateau where advancement becomes minor.

Also you don't need equal tech to pose a threat to minor outposts, just look at the Zulu wars, the British Empire launched a pre-emptive strike (well the local governor did without central permission) to remove the threat of the neighbouring Zulu army despite having massive technological superiority and nothing to fear in reality. The shear presence of the Zulu army made it necessary however to be prepared to deal with the potential threat, an unwelcome expense for the governor, who was also eager to grab some more land, despite it proving to be of no economic benefit.

As to the xenophobia being rational argument that seems to come up somewhat often in this forum. It isn't actually rational at all

I didn't intend to imply that it was the logical course for a civilization to pursue, but does have a real reason to make an alien government consider it as a course of action, even as an unlikely one.

it is very unlikely there would be any sort of ground, or even atmospheric, war

The idea of a ground occupation is rather ridiculous. Even with massive technological advantages the cost to occupy even just the major urban centres would be stupendously large, especially if troops can't be whooshed in at ftl speed.

[Samuel]

Because you have a tech and infrastructure lead that they can never catch up to.

We don't need to catch up to post a threat/problem. Simply by existing we are using resources and space that they could be, and once we do start to colonise other star systems that problem will grow exponentially over the millennia. Also it is possible for one species to catch up technologically with another, especially when they have become exposed to each other’s existence and trade/theft has begun to spread ideas, and that’s ignoring the idea of a technological plateau where advancement becomes minor.

Also you don't need equal tech to pose a threat to minor outposts, just look at the Zulu wars, the British Empire launched a pre-emptive strike (well the local governor did without central permission) to remove the threat of the neighbouring Zulu army despite having massive technological superiority and nothing to fear in reality. The shear presence of the Zulu army made it necessary however to be prepared to deal with the potential threat, an unwelcome expense for the governor, who was also eager to grab some more land, despite it proving to be of no economic benefit.

As to the xenophobia being rational argument that seems to come up somewhat often in this forum. It isn't actually rational at all

I didn't intend to imply that it was the logical course for a civilization to pursue, but does have a real reason to make an alien government consider it as a course of action, even as an unlikely one.

it is very unlikely there would be any sort of ground, or even atmospheric, war

The idea of a ground occupation is rather ridiculous. Even with massive technological advantages the cost to occupy even just the major urban centres would be stupendously large, especially if troops can't be whooshed in at ftl speed.

Except that we aren't using all the resources in the system. Primitive civilizations only occupy their home world, which is at the bottom of a gravity well- not worth bothering to mine due to the difficulties of pulling it out.

It is worth noting that the Zulu's aren't such a good example- they could actually get to the British. When you have space superiority, nothing a privative civilization can do can touch you.