Minimum invasion force level

[montypython]

If an alien species were to attempt to conquer Earth in the present day, what would be the minimal amount of force necessary for them to overcome human military resistance (assuming they'd desire the planet mostly intact if possible)?

[Samuel]

We need tech and goals to decide. After all, neutron bombs are "mostly intact". If they don't care they can simply herd the populance into arcologies and shut of the power for uncooperative sections.

[Bilbo]

Cannot determine that without some idea of the tech level of alien invasion force and their timeframe. Also need to know what you consider conquer. Are you talking the defeat of every military force on the Earth? That is alot more than just the claiming of major sections of the planet and holding it against human counter attacks.

Also need to know how violent the invaders are. If they plan on exterminating humanity and start immediatly then Earth has no reason to hold back and nuclear weapons will be used liberally which means the aliens need enough tech and size to stop nuclear arsenals from either being launched or stopping them in flight.

[Singular Intellect]

The question is far too vague in regards to the aliens. Hollywood has seemingly convinced most people that alien invaders would a force we could realistically fight, like an Independence Day scenario or War of the Worlds.

However any species technologically advanced enough to travel and deploy forces across interstellar space into our solar system with the intent to conquer it would look upon our military capabilities as utterly insignificant. It wouldn't exactly be unrealistic to assume they would have the capability to deploy billions of troops onto our planet if they really wanted to conquer it that way, assuming such a primitive method was still in their arsenal.

However, that would seem unlikely; if these aliens have any strategic or tactical sense as we understand it, they would simply cripple our entire planet with a surprise attack like massive EMP bursts to disable most of our technology in one swoop, and that's not even guessing at other technological wonders they would have at their disposal. Like artificial soldiers/weapon systems they produce at such a scale that we couldn't destroy them faster than they are able to produce them. You think our world production scales is impressive? Imagine if they have hundreds or thousands of world dedicated to just their war machine.

Another useful tactic would be a demostration of absolute force; obliterate a city or two of every significant power on our planet and demand unconditional surrender. They would have the ability to strike from orbit and destroy any pitiful counter attack on our part.

If faced with an interstellar alien power from space, the most likely conclusion is we would have two choices: annihilation or absolute subjugation.

[montypython]

Those are all good points (and Bubble Boy addressed some things I hadn't really thought about), so I'll make some clarifications.

For the considerations of a scenario, the example would be of a relatively small sub-light interstellar capable civilization (5 star systems or less), who wish to add more biologically sustaining worlds to their direct control, and as such do not wish to wreck the biosphere if it can be avoided. Their tech level is sufficient to sustain control of 5 or more star systems in a 100-ly radius, and their homeworld is about 10-ly away. Humans would be considered an interesting biological entity to study as a sort of 'informational bacteria' and thus population collection would be desired, but human concerns are irrelevant to their POV. Suppressing hostile action would be their focus, killing would merely be incidental to that effect.

[The Romulan Republic]

Assuming "realistic" tech for the aliens (ie, no ftl or energy shields), it depends on how you define "conquer." If the goal is simple extermination, they can use anything from dropping chemical weapons in our atmosphere, to lobbing in a couple asteroids, to massive nuclear bombardment.

If the goal is to control humanity without killing it, or to win a conventional war, it gets a lot harder. Isn't the current thinking that Bush should have used 500,000 troops for the initial Iraqi invasion? One little backward nation. Of course, the tech difference will make it easier on the aliens, but unless you allow for indiscriminent use of WMDs, the aliens will need "boots on the ground" (or whatever there equivalent of boots is). Shipping those troops across interstellar space without FTL would be damn near impossible. All the logistical advantages of the defender are vastly magnified in interstellar warfare.

[open_sketchbook]

Still super vague here. I'd suggest simply "Aliens have our tech, but the ability to ferry stuff from orbit via aircraft" as a good standard.

[Samuel]

Those are all good points (and Bubble Boy addressed some things I hadn't really thought about), so I'll make some clarifications.

For the considerations of a scenario, the example would be of a relatively small sub-light interstellar capable civilization (5 star systems or less), who wish to add more biologically sustaining worlds to their direct control, and as such do not wish to wreck the biosphere if it can be avoided. Their tech level is sufficient to sustain control of 5 or more star systems in a 100-ly radius, and their homeworld is about 10-ly away. Humans would be considered an interesting biological entity to study as a sort of 'informational bacteria' and thus population collection would be desired, but human concerns are irrelevant to their POV. Suppressing hostile action would be their focus, killing would merely be incidental to that effect.

Simple. Get a strand of Ebola, modify it to be airborne and sit back. 95% of the population dies in 2 weeks. That gives you 300 million humans to work with. Collect them all in a central location using powered armor and the planet is yours.

[Singular Intellect]

If the alien species in question is limited to sub light speeds, yet they still have the capability to ferry enough military forces to another star system for the purposes of conquering an entire planet, that capability alone suggests a massive industrial and technological advantage over us.

So we are either dealing with ridiculously stupid aliens (not likely if they figured shit out we haven't), or ones with such an industrial and technological advantage over us that it comes right back to my point of annihilation or absolute subjugation.

(as mentioned previously, orbital bombardment of biological attacks is just another effective means of killing off humans without them getting shot at)

Let's face it: even if we laughingly assumed their military technology is completely equal to our best stuff, it's being asserted they can deploy planetary occupation forces across interstellar distances at sublight speeds. That alone indicates their tranportation vehicles will have an enormous amount of self sufficiency, resources, technology and redundancy.

They will obviously be able to pick and chose their fights at any point on Earth where the situation favors them the most, all the while snickering at any pitiful attempt by us to fire a rocket or two at their massive orbiting vessels.

[Samuel]

Heck, even if they are not hostile, they can colonize the entire solar system and we can't stop them! Then we would truely be a subject species, aliens in our own solar system.

[montypython]

Still super vague here. I'd suggest simply "Aliens have our tech, but the ability to ferry stuff from orbit via aircraft" as a good standard.

I was working on the assumption of the aliens being about slightly ahead (about 50 years) in a given human tech as a reference point for a scenario like this, forgot to mention that, oops.

All the points raised do demonstrate well how fancy technology like force fields and planet smashing weapons really aren't necessary to seize a planet like Earth. Part of what got me thinking about this was that for all the advanced tech alien invaders in sci-fi generally have at their disposal they don't for the most part seem to use them very effectively, so looking at beings with excellent competency using relatively 'simple' technological means by comparison would be an interesting story to write up as a case in point. The closest stories I can think of in mainstream media like this would be "Roswell" and "X-files", although the latter may be questionable.

[Swindle1984]

Those are all good points (and Bubble Boy addressed some things I hadn't really thought about), so I'll make some clarifications.

For the considerations of a scenario, the example would be of a relatively small sub-light interstellar capable civilization (5 star systems or less), who wish to add more biologically sustaining worlds to their direct control, and as such do not wish to wreck the biosphere if it can be avoided. Their tech level is sufficient to sustain control of 5 or more star systems in a 100-ly radius, and their homeworld is about 10-ly away. Humans would be considered an interesting biological entity to study as a sort of 'informational bacteria' and thus population collection would be desired, but human concerns are irrelevant to their POV. Suppressing hostile action would be their focus, killing would merely be incidental to that effect.

Simple. Get a strand of Ebola, modify it to be airborne and sit back. 95% of the population dies in 2 weeks. That gives you 300 million humans to work with. Collect them all in a central location using powered armor and the planet is yours.

Airborne Ebola exists, and the strain very nearly got out into Europe once before the symptoms showed up in an infected traveler.

The disease kills people too quickly to be effective. There isn't enough time for it to spread. I'm not sure, but it may have died out simply because it killed the victims before they could infect many others.

[Starglider]

With sufficiently good nanotechnology;

A bucket of marble-sized von-neumann machines, distributed over the earth, which will self-replicate and manufacture medical nanobots, which will be introducted into food and water supplies. Once consumed, they will migrate through the body to the brain, network together and implant on key nerve sites. You can either have the aliens turn up and send a coded signal to stop everyone's hearts, or knock everyone unconscious. Or with only slightly better tech you can have the nanobots self-rep or just build up in concentration some more, form sentient AIs and take over everyone's brains. Earth thus becomes a slave planet for the investment of one dustbin sized interstellar probe.

So yeah you might want to quantify the alien capabilities.

[Samuel]

The disease kills people too quickly to be effective. There isn't enough time for it to spread. I'm not sure, but it may have died out simply because it killed the victims before they could infect many others.

Wasn't aiming for people to infect others- you can simply release enough to kill everyone who is unprotected on the surface.

I'm pretty sure nanotech can't do that starglider.

[Junghalli]

It's worth noting how the conquistadors managed to take out Mesoamerican civilizations with tiny numbers of men: gang up with natives who didn't like the biggest native power.

[Marcus Aurelius]

The disease kills people too quickly to be effective. There isn't enough time for it to spread. I'm not sure, but it may have died out simply because it killed the victims before they could infect many others.

Wasn't aiming for people to infect others- you can simply release enough to kill everyone who is unprotected on the surface.

It would be much easier to bioengineer the Ebola for a longer incubation time than to device a method for spreading the virus directly to the whole exposed population. Of course the latter could be done with sufficiently advanced tech, but it's certainly a non-trivial problem and would probably be that even for a species capable of sublight interstellar travel.

[Starglider]

I'm pretty sure nanotech can't do that starglider.

I'm pretty sure that it can, in the sense that the laws of physics don't rule it out, and that I know a few people I'd consider experts in the field who've told me that similar feats probably are possible if the technology was fully mature. Any particular reason why you think this is impossible?

[Samuel]

I'm pretty sure nanotech can't do that starglider.

I'm pretty sure that it can, in the sense that the laws of physics don't rule it out, and that I know a few people I'd consider experts in the field who've told me that similar feats probably are possible if the technology was fully mature. Any particular reason why you think this is impossible?

Where are they going to get the energy and the materials to make more of themselves? How are they going to survive in the open (UV is fatal to them)?

Simple solution are better- remember humans have radio waves which could set them off.

[Mr Bean]

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.

[Bilbo]

Those are all good points (and Bubble Boy addressed some things I hadn't really thought about), so I'll make some clarifications.

For the considerations of a scenario, the example would be of a relatively small sub-light interstellar capable civilization (5 star systems or less), who wish to add more biologically sustaining worlds to their direct control, and as such do not wish to wreck the biosphere if it can be avoided. Their tech level is sufficient to sustain control of 5 or more star systems in a 100-ly radius, and their homeworld is about 10-ly away. Humans would be considered an interesting biological entity to study as a sort of 'informational bacteria' and thus population collection would be desired, but human concerns are irrelevant to their POV. Suppressing hostile action would be their focus, killing would merely be incidental to that effect.

Simple. Get a strand of Ebola, modify it to be airborne and sit back. 95% of the population dies in 2 weeks. That gives you 300 million humans to work with. Collect them all in a central location using powered armor and the planet is yours.

Airborne Ebola exists, and the strain very nearly got out into Europe once before the symptoms showed up in an infected traveler.

The disease kills people too quickly to be effective. There isn't enough time for it to spread. I'm not sure, but it may have died out simply because it killed the victims before they could infect many others.

Doesnt matter. If you can travel between planets and you can manufacture Ebola then why would you infect one person with it and sit back.

Fuck no.

You would infect tens of thousands every day for a week or month. Your ships would fly over cities all over the world every day dropping packets that release it or spraying it in vapor form like a crop duster.

How quick ebola dies out can actually be an advantage. It would allow you to use it like crazy to kill of most of humanity while sparing certain remote groups of people to keep as "pets" or "research samples" etc.

[Samuel]

They are going to go for effective, not hyper fast. They had to get here sublight, remember?

[Coyote]

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.

[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.

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[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.