Scenario -- how would you invade the earth?

[jollyreaper]

The biggest problem with the standard invasion scenario is you have to have aliens with the tech savvy to cross lightyears coming to Earth and mucking about with us directly for some reason and being weak enough for us to conceivably fight back. That goes directly against what we really want to see -- military tech going nuts in a WWIII 'splosionfest.

As an alternative to aliens, how about a good old-fashioned parallel dimension invasion scenario. Let's say we've got a parallel Earth where the Nazis won WWII and WWIII. They own the blackened, irradiated remains of Earth. Yay for them, but the environment is screwed. They need some serious lebensraum. Lucky for them, their scientists have gotten dimension gates working. And what's on the other side? Our Earth.

Making up some ground rules, the gates have to be geographically situated where you want them to open. You want a gate in downtown Washington, Earth, you need to put a gate in downtown Washington, Nazi Earth. Presumably opened gates will need to be directly observed for anyone to know about them and it will take time for Earth scientists to figure out gate science and work up detectors.

So, if you were directing the conquest of Earth, what would you do?

My take on it is that it can go two ways, smart or dumb. Dumb would be an all-out attack from the start, gates opening an Nazis pumping units through, trying a planetary blitzkrieg. It would probably go nuclear very quickly and wreck this planet, too. But it sure would be cinematic. Smart would involve a long spy campaign to figure out just what's going on with this world before an open attack. There would probably be a well-organized campaign of terror and sabotage to soften up the place. Starting wars between powers that already don't like each other would be a good start. At the same time, the Nazis want to try not wrecking everything the way they did it on their Earth.

The sabotage campaign would certainly drive the spooks nuts. Here you've got terrorist groups coming in from completely off the radar hitting vital targets and nobody knows who they are. Well-trained, well-equipped, and fanatical.

The one really obvious tactic not mentioned so far is to open up gates right on top of someone's capital for a decapitation strike. Open a gate in DC, a gate at Cheyenne Mountain, push nukes through, the whole chain of command is in disarray. Of course, if the Russians are still running the dead man's switch they claim they aren't over in Moscow, taking it out like that would trigger an automatic first strike by every nuclear asset they have at their pre-selected targets. They're supposed to all be aimed at the south pole in case of an accidental launch but who knows if that's really the case. The only way to prevent this sort of thing from being employed is saying gates are really hard to construct so it's better to put them in isolated areas so that a large weight of troops can be pushed through before anyone notices. And the first thing through the gates would be super-SAM's capable of engaging bombers or incoming nukes since the obvious first reaction to an invasion like this is to just blow the hell out of the gate zone.

It's a crazy scenario, true, but still more plausible than imagining aliens flying lightyears to get to Earth and getting shot at with F-22's or actually landing alien grunts for us to shoot at with M-16's.

[Stark]

So your cunning attack on space alien invasion stories is a story with no aliens, no space travel, and few scifi elements? You're pretty smart.

Since the cybermen already did this, it's obvious that the effective method is to send a few scouts, locate critical areas, then deploy millions of guys all over the world simultaneously to attack the military while seizing civilian areas and declaring a fait acompli almost immediately.

[jollyreaper]

So your cunning attack on space alien invasion stories is a story with no aliens, no space travel, and few scifi elements? You're pretty smart.

If you strip the idea down to the basics, the alien invasion is an attack by an unknown enemy who can go toe to toe with your greatest fighting forces. There was always the WWIII scenario here on Earth before the fall of the USSR and the techno-thriller writers have been desperately searching for a new villain ever since. Hasn't been too fruitful. You can imagine a dozen brushfire war scenarios or Iraqistan low-intensity conflicts but there's simply nothing happening out there on a Tom Clancy scale.

Since the cybermen already did this, it's obvious that the effective method is to send a few scouts, locate critical areas, then deploy millions of guys all over the world simultaneously to attack the military while seizing civilian areas and declaring a fait acompli almost immediately.

Still doesn't account for the boomers at sea. Figure out a way to neutralize them during the big attack? How? Aside from the boomer question, that scenario works if you can place gates wherever you want and they're relatively cheap. If they're expensive and hard to place, a global sneak attack is not possible. And that does present a difficult scenario, trying to push modernish military columns out from the gates while facing attack by anything up to and including tactical nukes.

[Stark]

You mean except how the complaints about alien invasions centre on their possession of FTL, generally giant spaceships, the high ground of orbit, probably huge numbers etc, which aren't relevant here.

What are the SSBNs going to -DO-, idiot? Countries will have to surrender because you own their population centres. Are they going to nuke New York to get you out?

If you're invading anther planet through chokepoints, you're just going to wait however long you have to to have heaps, or you're a complete idiot.

[jollyreaper]

What are you, twelve? What's with the name-calling?

By your same logic, Japan wouldn't have attacked the US because any rational observer could see that no amount of fighting spirit could make up the shortfall between their industrial capacity and the USA's. Hitler never would have attacked the USSR because there was no possible way he could conquer a country of that size. But if he was going to, most certainly he'd plan for a proper long campaign and not just assume he could go the whole distance with summer uniforms. Or more recently, Rumsfeld ignored his generals when told how many troops it would take to hold Iraq because he knew there wouldn't be the political support for that kind of number. He could get the support for the smaller number and he told his generals that would be sufficient. And it was sufficient for taking the country and was insufficient for securing it, exactly as he'd been told.

There's plausible mistakes and inexplicable mistakes. Plausible mistakes are the blunders we see through history and, if given the proper context in a story, will make for tragedy. Inexplicable mistakes are the sort of thing that completely pull us out of the story and start doubting the ability of the writers. Strictly speaking, if the side that launches a war of choice loses it, someone miscalculated. I'm hard-pressed to think of many examples where nations started wars with the full expectation of losing.

[Eternal_Freedom]

If gates are easy enough to construct, then it is possible to have a decapitation strike, just a none nuclear one. But it takes a lot of gates. First off, intel gathering, find out where all the silos are, all the launch control centres, the bunkers for the VIP's and all the big ELf transmitters for the boomers ( I believe the US one is somewhere in Michigan)

Stage Two: Provoke multiple small wars and get larger nations involved, to dilute both their military strength and their attention. Note: serious enough to warrant significant military involvement but not serious enough to warrant forward-deploying nukes

Stage Three: open up gates as near simultaneously as possibly around all the silos, control centres, bomb wing bases and so on listed in Stage One. Deploy special forces teams to secure the targets. Launch similar strikes against the White House, the Pentagon, Cheyenne Mountain, Camp David and the Russian/Chinese/British/French equivalents. Capture if possible or kill the leadership if necessary

Stage Four, starting as soon after Stage Three as possible, deploy gates in major population cntres like New York, LA, Paris, Berlin, London, Moscow, Beijin, Tokyo and so on, deploy regular army units to secure the city and prevent anyone leaving.

If all that works, you have the enemy leadership wiped out or in custody, most of the worlds nukes secured by your troops, if not under your control, the communications cut off to the boomers (who if they are running deep and receive no mesages from the ELF stuff, may not know whats happenning until it's all over), and the major cities basically held hostage. And without using any nukes

Now that I think about it, once the nukes are secured they should be moved back to Nazi-world or destroyed/made non-functioning (trashing missile guidance system would work well I think) to avoid any nasty dead-man's hand stuff

[Purple]

Just a question.

If said dimensional portals exist what is stopping high command in Germania (Nazi post WW2 Berlin) from simply telling their scientists to pick a different destination like say Earth #34253 - The planet of fluffy bunnies instead of this over polluted, nuclearly armed, disunified hell hole that can't even support it's own population properly?

I mean, why not just pick a target that is softer?

[jollyreaper]

Just a question.

If said dimensional portals exist what is stopping high command in Germania (Nazi post WW2 Berlin) from simply telling their scientists to pick a different destination like say Earth #34253 - The planet of fluffy bunnies instead of this over polluted, nuclearly armed, disunified hell hole that can't even support it's own population properly?

I mean, why not just pick a target that is softer?

Good question. We could only assume they would if they could. Thus the inference must be that none of the other Earths they've found so far have been viable. Maybe they're lifeless balls of muck, maybe some have powerful non-human civilizations far in advance of our own like intelligent dinosaurs, etc. Unless they are insane, we can only assume they're attacking us because this is the best alternate Earth they've found. But it pretty much falls under the category of "because we wouldn't have a story otherwise."

[Eternal_Freedom]

Maybe they looked at other worlds, and decided that we WERE the softest targets,, because we are disorganised, spend our time fighting each other and so on. Maybe the other worlds where much stronger than we are, or uninhabitable due to a K-T event or a massive solar storm or WWIII or whatever

While you raise a good point about going to a fluffy bunny world where humans don't exist, I think the Nazi's would want to conquer a world that still has considerable human infrastructure ready made to exploit. It doesn't matter that we might not be able to support our population, they can always reduce that

[Rabid]

I was thinking... I know that you want an invasion scenario, but...

You say that the nazi world is burned. This mean that there possibly can't be so much available population - 1 billion, 2 billion at the most. Long story short, the chances of success of a invasion are greatly reduced.

Now, I know that the NAZZIES weren't known for being logical (or that their logic was misguided), but I think that there would be a much sensible thing to do.

What can it be ? I'll tell'ya :

TRADE

After spying us, they'd see that we have a number of tech that they could apply to their wasteland. Things like biodome, hydroponics, genetic engineering, whatever. In return, they have the mineral resources of a depopulated earth to trade with us. If they put aside such things as "ideology", they could, maybe, obtain more benefit this way than with an invasion.

Plus, they now know a way of traveling between dimension. This mean they could engage in trade with other civilization, become a nexus of interdimensional trade for the Earth-Zone, maybe even buying the technology enabling FTL travel somewhere, and after that expanding in new territories, forming a multi dimensional realm.

Plus, they could harvest the resources of the Dead-Earths as well.


I tell you : they would benefit far far more from a trade approach than from a war one. But, eh, we are talking about NAZZIES her. They will just attack with might, win for a while, and then get their ass handed to them when the winter come. And after that, we exploit their technologies, build weapons with it, but never colonize space with it because... just because.

[Zaune]

Assuming I was committed to this world, and had to go to war with whatever forces I had instead of what would be necessary for simultaneous knockout strikes, I'd start small and work my way up. Africa would be my destination of choice, as it's a relatively soft target with plenty of national resources and few overseas allies, and limited potential for serious resistance. Inter-dimensional portal technology offers all kinds of interesting possibilities for outflanking and infiltration that someone considerably smarter than me covered exhaustively elsewhere on the board, so I shan't rehash them here.

Once we were at the end of major combat operations there, Phase Two would be to establish forward airbases and dig in to protect my supply lines from counter-attack, install local leaders who'd do what they're told and turn the industrial might of the home nation loose on the local natural resources to offset the appalling bills I'd run up thus far. I'd also be using my engineers and medical corps for hearts-and-minds projects in the really FUBAR parts like Somalia or Darfur, with film crews recording said projects and uploading the footage to YouTube.

These would lead into Phase Three: Recruiting, training and equipping from the local population, possibly with locally-produced equipment if there's enough left of South Africa's defence contractors. Most could be used as decoys regular line infantry for the next target -probably Europe- but existing somewhat organised groups could keep their command structure and recruitment policy and be used as fifth columnists; imagine portal-deploying the West Side Boys into south-east London three weeks before a ground invasion!

After that, I'd pretty much rinse and repeat until the process of conquest was done with, then retire with a chestful of medals and the satisfaction of knowing that holding onto the place was someone else's problem.

[Stark]

What are you, twelve? What's with the name-calling?

By your same logic, Japan wouldn't have attacked the US because any rational observer could see that no amount of fighting spirit could make up the shortfall between their industrial capacity and the USA's. Hitler never would have attacked the USSR because there was no possible way he could conquer a country of that size. But if he was going to, most certainly he'd plan for a proper long campaign and not just assume he could go the whole distance with summer uniforms. Or more recently, Rumsfeld ignored his generals when told how many troops it would take to hold Iraq because he knew there wouldn't be the political support for that kind of number. He could get the support for the smaller number and he told his generals that would be sufficient. And it was sufficient for taking the country and was insufficient for securing it, exactly as he'd been told.

There's plausible mistakes and inexplicable mistakes. Plausible mistakes are the blunders we see through history and, if given the proper context in a story, will make for tragedy. Inexplicable mistakes are the sort of thing that completely pull us out of the story and start doubting the ability of the writers. Strictly speaking, if the side that launches a war of choice loses it, someone miscalculated. I'm hard-pressed to think of many examples where nations started wars with the full expectation of losing.

What the fuck are you TALKING about? If you woke up tomorrow and every major US city and military base was controlled by Space Nazis, what the fuck do you seriously expect anyone to do about it? Use SSBN magic to destroy the US in order to save it? I don't give a fuck about your history lessons or your creative writing classes. You asked how you'd do it; I told you it was done years ago. Cybermen are cooler than nazis anyway.

The idea of an interdimensional threat taking over Africa (great target there) and controlling it while at the same time alerting the entire world to the threat and giving them time to counter it is ridiculous.

[Purple]

I don't think you even have to waste troops on that.

Consider this scenario for a moment.
I can open dimensional portals anywhere I want right? That also means in the middle of a major city.
The first thing I would do is send out agents and spies on a multiple years worth mission, maybe even a decade to establish data about the local powers to be. What that is done I would do is send an emissary to each of the more important nations. These emissaries would be trained but otherwise completely expendable (like not knowing how the transporter works and fanatical) and their mission world be to use any and all means at their disposal to send out a clear message. Think something like this:
"In 1 year, the great empire from beyond this earth will come to conquer you. By that time, all countries have to surrender. Any that do not shall be annihilated."

Naturally, I don't expect anyone to surrender with just a threat. Hence, I would use the portals for a series of demonstrations. Killing the families of rich people/officials, placing nuclear bombs in major cities etc. Once the enemy is scared so much by the realization that I can do what ever the heck I want and there is nothing they can do to stop me I simply walk in and they surrender. After all, who wants to be the target of random nuclear bombing for fun?

[Zaune]

The idea of an interdimensional threat taking over Africa (great target there) and controlling it while at the same time alerting the entire world to the threat and giving them time to counter it is ridiculous.

Yeah, but the idea of an inter-dimensional threat taking over the entire world is ridiculous anyway, so what the hell.

More seriously, I have no idea of the precise numbers you'd need to mount simultaneous air and ground attacks on every major military on the planet that had a fighting chance of success, but the logistics of it would make this scenario as implausible as a standard alien invasion plot. A plausible Nazi-dominated alternate Earth would have a choice between spreading itself so thin that they'd find themselves trying to take over the entire state of Texas with a single battalion, or concentrating on one region at a time and making do without strategic surprise.

And I stand by my original justification for Africa as a beachhead, though I can see it would have plenty of drawbacks. The more reason the appeasers, the not-our-problem brigade and the merely exhausted by bloody and inconclusive foreign adventure have to argue against intervention, the more time there is to plan for a decisive campaign against a more dangerous opponent.

I don't think you even have to waste troops on that.

...

"In 1 year, the great empire from beyond this earth will come to conquer you. By that time, all countries have to surrender. Any that do not shall be annihilated."

You're not going to be left with much worth conquering if they call your bluff, though.

[Stark]

Are you insane? You need to decapitate maybe six countries to remove 99% of the military of the world. The Space Nazis rule their entire planet, remember? They will clearly be more militarised and have the initiative.

Then again, you appear to think that holding civilian populations to ransom by annihilation would be hard, which is very strange. They can even destroy whole cities at no risk to themselves, because they're safely in another fucking dimension!

[Purple]

If they call my bluff, I can always go with the whole kill 1 hostage per month/week routine. Just replace kill with nuke and hostage with major city.

After all, I will want the planet depopulated anyway to make sure my colonists have a self sustained future. As such, I would probably go for neutron bombs. Oh, and since I am Nazis I get to nuke Israel out of existence to make a point that I mean it. (if that is not making a point, what is. As inhumane and disgusting as that sounds it is what they would do in character)

[Stark]

Every city or military base you sieze by surprise strengthens your hand and makes it harder to be dislodged; even if you just seized the American northeast, the massive brutality you're prepared to visit and the escape of the gates makes your position solid.

Holding the area is a different story, but that's where Space Nazi extortion comes in.

[Purple]

So a combination of our plans.
Yes, that would probably work best.

[Rossum]

Question: Do the space Nazis have access to germ warfare?

If so then they could start engineering anthrax and swine flu and all sorts of nasty shit. Then they open up portals all over the world and start dumping the germs in the water and food supply (possibly infiltrating various major food companies and such). Instead of using nuclear weapons that result in radioactive zones, they use germ warfare that kills people and can conceivably be stopped with some inoculations.

Then just wait for the plagues to wipe out large portions of the population or weaken the military/economy/whatever until the nations are weak enough to conquer. After attacking the major military, economic, and government centers, they can announce to the survivors "We have conquered your military, your leaders are dead at our feet, our plagues are running through your population like wildfire. Resist and you will be exterminated, surrender and you will be given medical treatment and a place in our glorious new world order (as our slaves). ... oh, and if you prove to be too much trouble to conquer then we will just infect your cattle and crops and destroy all your medical facilities so you all fucking die in agony without us having to lift a finger. Then, we'll just retreat to our home dimension and come back in a few months once you've learned your lesson."

Basically use germ warfare to soften up the population before invading in force, preferably make the diseases look natural or blame somebody else for it so that nobody expects parallel universe Nazis of being responsible. Then go through with other invasion ideas and use the disease outbreaks as leverage to weaken various nations and blackmail people into giving stuff up for the vaccinations. If the invasion proves to be a bust then contaminate lots or populations, the food supply, and blow up whatever Earth medical research stations you know about. Then retreat into your home dimension while the germ outbreaks work their magic and come back later after social problems further weaken the nations (maybe keep spies around to make sure and kick people when they are trying to recover).

So if you can't conquer the world on the first try then feel free to mess up their economies and leave a bunch of super viruses all over the place to make their lives a living hell until you decide to attack again. Always keep the vaccines on the bargaining table to further encourage people to surrender.


Oh, and another possible avenue to explore would be to locate oil wells or other deposits of liquid resources and use portals to steal it out from under peoples noses (I don't know if that's even possible but might as well toss it in). Basically find out where major oil wells are on the target Earth, then build a corresponding well on Nazi Earth, then set up some kind of portal thing where they drill from Nazi Earth goes to Target Earth and rapidly starts sucking up all the oil out of the deposit. Net result is that Earth runs out of cheap oil that much faster while Nazi Earth gets resources. I suppose it would be cheaper and more practical to just target the wells on one of the first strikes but doing it covertly like that could work to weaken Earths economy first while boosting their own and letting the people of Earth think they had just used up all the oil by themselves.


And if you REALLY want to be impractical and evil then I suppose you could have spies infiltrate various religious nations and start cults that prophecy that the END OF DAYS will be coming with angels and demons fighting for the salvation of mankind. Have minor miracles or whatever get followers and then when the invasion starts then tell the followers to meet up at certain locations to be saved from the Apocalypse. Then, open up some portals, have the crowds run inside, and have a huge gas chamber/meat factory on the other side to kill them. Or I suppose you could use the loyal followers for other stuff like give them positions of power over the conquered massed but whatever.


I suppose using the portal network to smuggle drugs pre-invasion would be worth investigating? I mean if you've got a whole planet on your end and portals to pull off an invasion then you could use your system to smuggle drugs, weapons, and stuff across boarders. Make contact with criminal organizations or terrorist groups to get info and use your system to buy and sell drugs and weapons to/from them. Might not want to let them know the secret of your system but be sure and let them profit from your relationship. If your Nazi scientists want to invent new and more potent drugs to get people addicted to then that could do something for your conquest of Earth.

Actually, if you can pull off a smuggling system with portals to bypass Earths borders then you could make money that way and then conceivably buy whatever it is you need from Earth to begin with. Make contact with them in that way, do some underhanded stuff, if anyone finds out then show them your ruined Earth (make them think that you are militarily weak if you want) and tell them that you have no choice and don't want to be attacked. That could at least give you access to some allies on the Target Earth and provide intel for the invasion if you need to go that route.

If they attack you then you could pull off the invasion while declaring that you have no choice but to do so to protect yourself from the much richer Target Earth. Could score some sympathy points somewhere which you can then exploit for all its worth. Though hopefully the smuggling route thing would be done in such a way that it doesn't tip anyone important off before invasion.

[jollyreaper]

Not space nazis, parallel dimension nazis. Gotta keep your nazis straight.

Actually, the problems facing a conventional parallel dimension nazi attack are the same problems facing the conventional WWIII scenarios from the Cold War. Ok, so the fighting starts out without nukes. The USSR wants control of Western Europe, the US and NATO wants to prevent that from happening. You have two likely outcomes -- either the Russians are pushed back into their own territory or they pull it off. So what then? Do we really think it's likely that the US would accept that outcome, all of Europe going communist? Or the other way around, would the Russians really accept defeat without going nuclear?

There's no way to know for sure without actually fighting the war. But if we look at how close we've come historically to actually launching nukes historically, and if we consider that this was without WWIII being officially on, how much more likely would it be to launch when the knife is at your throat?

Now I've read analyses and scenarios by contemporary generals imaginging just how such a campaign would go, a WWIII that didn't end in global nuclear war. It just seems too unlikely. It seems as unlikely as the city-swapping scenarios MacNamara worked out, the sort of thing depicted in Fail-Safe. "Ok, so if we accidentally nuke one of their cities, we'll purposefully nuke one of our own of comparable size and importance. It'll be so reasonable." Yeah, I'm sure they'll see it that way.

Anyway, if we're telling this story and want cloak and dagger and decapitation strikes, multiple easy gates is the way to go. If it's hard to open gates and we'll say it took the parallel dimension nazis years to open each one, then barring the beachhead that could appear mid-continent, the campaign would subsequently play out a bit more conventionally with the nazi forces having to manuever across the surface just like the defenders.

There was a valid point above that the nazis could be in rough shape but German soldiers in WWII tended to be more skilled and eager than the drafted civilians of the western armies. I seem to recall some lopsidedly ridiculous kill ratio of like 10 to 1 against the Russians in the retreat back to Germany. Part of this is probably because the Russians had no regard for the lives of their troops vs. the western armies who had to be concerned with such things like morale and public support for the war effort.

Still, the original idea was to have big honking dramatic battles with high-tech equipment. So why would the Nazis be forced to move before they could do all the things possible to make this a short, victorious war? Maybe the defenders get a lucky break. Maybe Earth finds out about the gates and the plot and the industrialized nations immediately begin a military build-up. Having lost the element of surprise, the Nazis now have to attack as soon as possible before the entire world is retooled. So you might get a solid attack in on the American industrial base and decapitation attempts on Russia and China but the rest of the world remains intact. You end up with an American government in exile in the UK with survivors from the American defense industry bringing plans with them for the latest weapons. There would be a hell of a political fight as the major nations tried to hash out a proper military alliance, put together a unified command structure, figure out what their strategy will be. China, India, and Japan might end up being the "arsenal of democracy."

Imagine the tizzy if all focus is on the Nazi beachhead in the US and suddenly one opens up in China. If the defenders have no understanding of the gate technology, they could assume gates could open anywhere at any time and they would waste precious manpower securing areas that aren't actually under direct nazi threat.

Meanwhile, back in the States, you could have your Red Dawn scenario in occupied territories, guerrilla warfare and all.

Of course, there's also the question of naval combat. The Nazis would probably want to concentrate at first on sea denial rather than sea control. The question is whether or not a u-boat could fit through the gate. Being able to sink anything the defenders could float would be a pretty huge advantage in protecting the US holdings from counter-attack.

As for the other comment above about it being smarter for the nazis to trade with us instead of attack, yes that would make more sense. But we're talking about parallel earth nazis, not parallel earth reasonable people. Otherwise the title of the whole thing wouldn't be "invade the earth."

[jollyreaper]

Question: Do the space Nazis have access to germ warfare?

If so then they could start engineering anthrax and swine flu and all sorts of nasty shit. Then they open up portals all over the world and start dumping the germs in the water and food supply (possibly infiltrating various major food companies and such). Instead of using nuclear weapons that result in radioactive zones, they use germ warfare that kills people and can conceivably be stopped with some inoculations.

You get into the smash vs. conquer the planet argument that we get in the regular scifi discussions. Wrecking the enemy's planet is easy, just smack it with big rocks or reletavistic kill vehicles. Planet gone, declare victory and go home, no ground troops needed. It's a different story if you need it intact. Seeing as the parallel earth nazis succeeded in wrecking their planet with total war, they might want to proceed more cautiously, especially if it's really, really tough to find parallel planets. If it's very easy, they could try any number of approaches and invade the Earth that softened up the best.

Being paranoid nazis, though, they're going to wonder "if we figured out this trick, how many other parallel empire builders are out there?"

Then just wait for the plagues to wipe out large portions of the population or weaken the military/economy/whatever until the nations are weak enough to conquer. After attacking the major military, economic, and government centers, they can announce to the survivors "We have conquered your military, your leaders are dead at our feet, our plagues are running through your population like wildfire. Resist and you will be exterminated, surrender and you will be given medical treatment and a place in our glorious new world order (as our slaves). ... oh, and if you prove to be too much trouble to conquer then we will just infect your cattle and crops and destroy all your medical facilities so you all fucking die in agony without us having to lift a finger. Then, we'll just retreat to our home dimension and come back in a few months once you've learned your lesson."

If the Earth leaders suss out that the nazis are needing a new home here, they could hold the planet hostage. "We're fitting cobalt jackets to every nuke we have and will blow them if you don't back down." Given that we already know what life was like under Earth Nazis, they can assume life under parallel Earth Nazis wouldn't be any nicer. Death is preferable.

The danger of divide and conquer is if the war gets too hot before the attack. Does no good to get the nukes flying and leave this planet irradiated, too. They already have a nuclear wasteland Earth.

Or you could speculate that a minor nuclear war isn't all that bad, the Nazis can afford to wait it out, it was something far worse that rendered their planet unfit for habitation. Maybe that could be the superplague or maybe some genetically-engineered algae that's spreading like kudzu and will not be eradicated. Whatever the problem is, dealing with some fallout on a new Earth might seem like a reasonable trade-off.

Oh, and another possible avenue to explore would be to locate oil wells or other deposits of liquid resources and use portals to steal it out from under peoples noses (I don't know if that's even possible but might as well toss it in). Basically find out where major oil wells are on the target Earth, then build a corresponding well on Nazi Earth, then set up some kind of portal thing where they drill from Nazi Earth goes to Target Earth and rapidly starts sucking up all the oil out of the deposit. Net result is that Earth runs out of cheap oil that much faster while Nazi Earth gets resources. I suppose it would be cheaper and more practical to just target the wells on one of the first strikes but doing it covertly like that could work to weaken Earths economy first while boosting their own and letting the people of Earth think they had just used up all the oil by themselves.

Depends on how fancy you want to get with the portal tech. My preference would be to say it's really hard to get one working and you can't just move it about. Maybe say construction is an effort of comparable difficulty to the Chunnel and while you can certainly build another Chunnel, it's not an easy undertaking.

I think the biggest threat anybody with portal tech in this situation would see is that it's not that hard to figure out, it's within the technical reach of other civilizations if they're pointed in the right direction, kind of like the a-bomb. There was skepticism before it was built even though many scientists knew about the theory. Once the US had it, proof of concept, now everyone knows it can be done and everyone wants one. Once Earth sees portal tech in operation, our scientists start scratching their heads and eventually figure out how it must be done. A short-term advantage for the invaders only.

Actually, if you can pull off a smuggling system with portals to bypass Earths borders then you could make money that way and then conceivably buy whatever it is you need from Earth to begin with. Make contact with them in that way, do some underhanded stuff, if anyone finds out then show them your ruined Earth (make them think that you are militarily weak if you want) and tell them that you have no choice and don't want to be attacked. That could at least give you access to some allies on the Target Earth and provide intel for the invasion if you need to go that route.

I'm thinking of Austin Powers were Dr. Evil is upset that his empire is making billions of dollars but doing it legally. He wants to make money evilly, doesn't care about profit. Parallel Earth Nazis want military conquest, they don't wanna be gangsta narcos. lol

[Eternal_Freedom]

Then just wait for the plagues to wipe out large portions of the population or weaken the military/economy/whatever until the nations are weak enough to conquer. After attacking the major military, economic, and government centers, they can announce to the survivors "We have conquered your military, your leaders are dead at our feet, our plagues are running through your population like wildfire. Resist and you will be exterminated, surrender and you will be given medical treatment and a place in our glorious new world order (as our slaves). ... oh, and if you prove to be too much trouble to conquer then we will just infect your cattle and crops and destroy all your medical facilities so you all fucking die in agony without us having to lift a finger. Then, we'll just retreat to our home dimension and come back in a few months once you've learned your lesson."

Incidentally, this reminded me very strongly of what the Daleks do in "The Dalek Invasion of Earth" - inflict massive pandemic, wait for human civilisation to be crippled, then invade. Even the bit about surrendering to be slaves is in there, as is the threat of extermination if they resist. And, of course, the Daleks are based on the Nazis...

[Stark]

Except they come from space, have a stupid plan and don't just take off and 200 gigaton pew pew resistance?

[Eternal_Freedom]

What part of "based on" did you not understand? And also, your sentence afte rthe first "and" doesn't make sense

[jollyreaper]

After ruminating a bit, I've come up with a scenario I'm happy with. This is by no means the only scenario, you can tweak the variables any way you want to make things different. This is is my take on it.

1. Parallel Earth Nazis (hereafter called nazis) have Hitler die early in the war so it's subsequently operated by people a bit more rational, at least by nazi standards. They're still high-functioning psychopaths.
2. Nazis defeat the USSR, decide to go to war with the US after the development of the atom bomb. They can't tolerate the idea of someone else having a super-weapon of such power.
3. There's never much of a chance to build a world-ending arsenal of atom bombs and this happens before ICBM's so the 40 minute war never happens. It's a matter of sending intercontinental bombers to hit major targets, defended by fighters and possibly nuke-tipped SAM's. Very 1950's. The war drags out for years but the Nazis eventually win.
4. Nazis continue weapons development even after controlling what's left of the world because, as I said, they're psychopaths.
5. Succession crisis leads to Nazi civil war. The previous nuclear war had caused significant damage to the planet and the civil war seals the deal. They're screwn. I'm thinking of some sort of slow-motion ecological collapse where the best projections show diminishing returns over the coming decades and eventual collapse of civilization. This is not something they can possibly wait out and not something they can fix. Alternatively, it might be something they could out-wait but, being insane, they'd rather go with the cross-dimension invasion rather than do the sensible thing.
6. Nazi scientists crack the dimensional portal problem and start exploring. The results of exploration are that it's a) really, really tough to find a viable dimension to invade and after thousands of attempts of finding dead Earths ours is the only one they've found with a viable biosphere -- and a ton of residents. b) Portals are ridiculously expensive to build so they can only afford to build a few. c) They have to be built on Nazi Earth in the same spot they're supposed to appear on our Earth. d) Did I mention they're expensive?

So with that starting basis, here's the invasion plan. The winners of the Nazi civil war were the fanatical side. Measure and reason are not their calling cards. They must conquer and command, they will never accept the idea of negotiating or simply trading for resources. It's a national death cult.

1. Send spies through to figure out what they're dealing with.
2. Adopt a divide and conquer strategy. They have advanced weapons compared to the current state of the art on Earth and their society is like North Korea with a freakishly disproportionate number of people under arms but they lack the economic power potential of our Earth. They're a strong force of immense power but they would drown under the combined military forces of our Earth if we decided to go all-out war and turn our full industrial might against them.
3. World situation heats up as the shit gets stirred. Initial assumption is that it's the usual suspects but intel agencies feel that it doesn't quite smell right. Given our current geopolitical situation, the likely suspects are stirring shit between India and Pakistan, China and Asiatic neighbors, US and Russia, and general Islam vs. West crap.
4. Dead nazi agents really throw the agencies for a loop. They don't know they're nazis, there's just shit that doesn't make sense. Nazis are deliberately using native gear but if there's a lucky break and they roll a command cell, they'll find electronics that came from Nazi Earth and will completely perplex native intel agencies because the devices don't even look like they were built on Earth.
5. Terror campaigns ramp up and it takes a long time for the intel agencies to figure out what they're dealing with because it seems so outlandish.
6. A headslappingly lucky break clues our Earth in to what's actually going on with the Nazi plan. It's about on par with General Lee's battle plan getting lost in the field and picked up by the Union before Antiem.
7. The Nazi plot was predicated upon weakening our Earth's major powers before they invaded openly. They cannot allow our Earth to militarize and actually prepare to defeat the invasion. So the Nazi hand is forced and they invade before they would have wanted to for fear of invasion eventually becoming completely impossible.
8. Nazis invade and have very good laser defenses. Net result is that airborne targets can't really get near them at all. You can't nuke them with ballistic weapons, you can't get bombers over their rear areas, even artillery shells require extra-heavy barrages to saturate the defense. The only way to hit them is to go on on the ground with infantry and armor.
9. Nazis invade Earth from two or three beachheads. They make the US a priority and nail our industrial centers but, seeing as they moved prematurely, they were not able to decapitate the other major powers in the world.

The net result of all this is that the conflict could go either way. The stage is set for lots of pitched battles between equally-balanced forces with plenty of 'splosions and room for drama.