How would you invade a planet?

[Agemegos]

Originally Posted by Dangerious P. Cats

Assuming....

...biological weapons are not terrible workable.

Originally Posted by zoncxs

Find a virus that humans are immune to or can't get effected by but is lethal to the aliens and bombard them with it.

Where would you look? And what if there isn't one readily to be found?

I would genetically mutate it so that is can travel by air, water and contact and survives for only a few days.

That might be a big ask, depending on the properties of the virus you start with. At TL8/9 it sounds like a significant R&D exercise rather than a routine lab procedure.

[Johnny1A.2]

Originally Posted by David Johnston2

My invasion plans start with finding a set of local allies to play off against those those who won't play ball and landing there. That's how most successful colonization ventures work.

This^^.

More specifically, it depends on why you're invading. What do you want? Settlement rights? Trade concessions? To use the planet as a refueling station for further traveling? To deny access to somebody else?

What is the point of the exercise?

Picking your proxy is an art form, and it depends on your agenda. You want somebody who is sympatico enough with you that you and they can work together without constant backstabbing or upheaval, and who is sympatico enough with their world that being ruled by the proxy is tolerable.

(In practice, you may well need more than one proxy.)

It also depends on how much independence you're willing to cede to your proxy. It's probably best if the proxy power can actually do most of the real day-to-day ruling and administration, letting you be perceived not as the overlord but as an off-world ally of the dominant power.

There's likely to be a big psychological difference between you conquering the locals with orbital bombardment and landing forces, and locals conquering their neighbors with weapons you gave them (or sold them for $1.00 and considerations). Or even better, if the locals can conquer their neighbors using local weaponry but superior logistics and communication and transportation from you. The less local blood you personally shed, the better.

There are lots of real-world historical examples to draw on here, esp. from the 19th and 20th centuries, and from Roman times (among others).

It's going to depend on the local political/cultural situation to start with, too. For example, imagine the difference between an invasion of Earth in 1914 and one today (assuming 1914 also had TL8 tech). The details of the political side would be very different. Or say, 1975, when it would be very different from either 2014 or 1914.

For ex, in 1914, the aliens might throw their weight behind Britain, already the top power at the time, with experence at that role, and make them nearly unassailable. Or they might back Germany, who have an interest in dealing with Britain. Or they might work through America, (though at the time American isolationist impulses would be problematic), or they might pick a colonial people to back as a rebel force, or some combination.

In 1975, they might offer to protect either America or Russia from the other's nuclear strike capacity. Sit in orbit, pick off the ICBMS and bombers and sea-launched missiles of one side. That alone at that time would make either the USA or the USSR utterly dominant in the world, since the ally power could wipe the other at will.

Today in some ways is more like 1914 than 1975, but there are still significant differences.

This is a case where the details really, really matter.

[Grouchy Chris]

Originally Posted by Dangerious P. Cats

The reason for the invasion is that the planet has breathable atmosphere and compatible Eco-systems that your superiors want mostly in tact.

Given this, I am going to assume that all you want to keep is a functioning ecosystem, and genocide of the sapient natives is not a problem.

While rudimentary translation of the major languages is possible you also have little intel to go off.

And given this, I assume that taking the time to get better intel is not an option, or you wouldn't have made it a part of the scenario. Fair enough.

So, what are your invasion plans?

First, a lot of orbital bombardment. Identify the top-tier nation-state and its allies. In the initial strike, knock out their nuclear capabilities. Then, over the next ten days or so, use 10% of your tungsten orbital bombs to destroy major population centers, but keep it somewhat random. Bypass some of the fatter targets to hit smaller ones instead. Your goal is to cause panic in the civilian population so that they evacuate their cities, not knowing where the next bomb will fall. In this way, you get the enemy to effectively destroy his cities for you.

At the same time, use another 20% of your arsenal to target transportation and electricity production. Since these can't be moved, no need to drag this out, but if you can only drop so many bombs at one time, don't let this delay your terror bombing too much.

Now find the areas of the planet that have the most favorable ratio of ecological riches to military power. In Earth terms, this means Africa. Begin your ground invasion here. Give this area the same treatment as you did the first-rank power, but at a lower intensity, because there's not as much to hit here. This will take maybe 5% of your orbital bombs. The goal of the ground effort is to occupy as much of the biosphere as you can with minimal effort, so avoid pitched battles. Your major weapon is letting most of the population starve.

Over the next year or so, continue bombing population centers, expending another 20% of your arsenal. If any of the second-tier powers have put up any resistance to what you're doing, add their cities to the target list.

Do not worry about engaging the ground forces of the first-tier power and anyone else who has thrown in with them. By this time, you have smashed their ports, airports, highway and rail links, and power generation. Most of their political and military leadership is dead or ineffective because you've destroyed or depopulated the cities. They don't have any way to get their ground forces to your occupation zones, nor any fuel to operate there if they did. Just let them starve where they are.

You now have 45% of your orbital arsenal left for contingencies, and you can start planning the second year's ground invasion, targeted on another ecologically rich and militarily poor area. In Earth terms, this would mean either Amazonia or Indonesia, I suppose.

[Phoenix_Dragon]

I'm going to assume you want purely military tactics, rather than subterfuge and the like. By the sounds of it, the only thing the invaders care about is the ecosystem, so infrastructure is irrelevant.

The first and most important step would be: don't invade.

You've got the ultimate high-ground. You can strike with impunity, and they will be completely incapable or retaliation.

So the first step is to simply move into a medium orbit, high enough to stay out of their primitive ASAT range (So, a few hundred miles), and monitor everything. Gather visual and elint data. Plot every single military installation.

Then blast the crap out of them. You won't need strategic-nuke level kinetic hits, just a few kiloton-range impacts deployed against every single military installation as simultaneously as possible.

Then take out any launch facilities, for good measure. What little space presence they have will get stripped out by your ship-to-ship weapons as soon as the shooting starts. Then hit any naval forces that could be a potential threat, such as carriers, battleships, and missile cruisers.

At this point, you can move in with no threats. If you land troops, you can bombard any enemy forces who attempt to engage them, and your ships can strike any aircraft you might have somehow missed. Hit every port, airport, and rail-yard that you can, and watch as most of the population dies over the next few weeks. But really, you might as well just bombard every single population center. Again, no need for megaton-range impacts, we don't want to kick up enough dust to cool the planet notably. Just a few kiloton-range strikes.

If you've got lasers capable of hitting ground targets, then it's even better, as most of the above shooting can be done without any ammo expenditure.

[Dwarf99]

Originally Posted by Agemegos

Technical quibble: <snip>

Fair enough

[jason taylor]

Originally Posted by Agemegos

I think His Immensity the Leader has ordered "Invade" and no-one dares to question his orders.

Far be it for this worthless and dishonorable person to question the Will of His Immensity the Leader. I would however like to know what his specific objectives are because I cannot properly add to his glory unless I am aware of such things, however much they might seem beneath His Immensities attention.

Now are there resources on the planet or does His Immensity just want a Starport to carry transit traffic? In the second case all that is needed is to set up a base. In the first case those resources are easiest obtained by plugging the planet into the interstellar trading network which is also easiest done with one base. If in fact His Immensity wishes political rule over the planet then once we have a base we can slowly gain such rule over generations.

But then I suppose such concerns I have mentioned are the toys of tradesfolk and unworthy of the concern of His Immensity. Very well. I shall take a force, land it and create a series of fortified LZs from which to spread out. If the rebel scum who resist His Immensities rule possess no WMDs I can guarantee our foothold until reinforcements arrive and might even convince some of the population to yield before his splendor. If not I shall have to strike out from the LZ's to keep the rebel scum off balance. In the meantime I worthless and dishonorable though I am, I shall have to beseech His Immensity to empty the whole sector of troops and send them to my command, that they might be used to smite the enemies of our leader, because as small as planets are compared to the glory of His Immensity, to a mere lowly admiral such as this worthless and dishonorable person, a planet can be a big place.

[David Johnston2]

There are two basic options. Treat the natives like people, in which case the invaders must learn about them and communicate with them in order to exploit them, or treat the natives like vermin, in which case they target an impactor on every identifiable military installation and large population center to reduce the population as much as possible before moving in.

[Anthony]

Originally Posted by David Johnston2

There are two basic options.

Well, basic non-cinematic options. You also have options such as 'treat the natives as delicious'.

[Agemegos]

Originally Posted by jason taylor

Far be it for this worthless and dishonorable person to question the Will of His Immensity the Leader.

Indeed. The panjandum of the Splenetic Society is in only three cycles, and his Immensity doesn't want to get stiffed with the vice-presidency of the Dining Committee again. A seat on the Outrages Committee must be ours at least, and for that we need to be able to boast more invasions than the Oontnadatta. For the Immensity of the race! So get to it, Admiral. Ask "how high?" on the way up.

[Figleaf23]

Here's an idea.

Send a big rock from the sky to really give a good hard smash to civilization.

Then miraculously show up posing as the interstellar Red Cross. Use wealth, influence, secret force, and an aura of wisdom and helpfulness to control things from your Green Zone, while in reality setting the conditions for endless internecine conflict.