One of the oldest subgenres of science fiction is the AlienInvasion. Monsters from another planet come to Earth to eat our brains/mine our planet/terraform and colonize the Earth. If you're looking to write an alien invasion story, keep reading.

!'''Necessary Tropes'''
MilitaryAndWarfareTropes are useful when writing about an invasion. AlienTropes are the other half of it.

Bare necessities from the first group: EarthIsABattlefield, of course. If you want to make your story big, go for ApocalypseWow and BigBadassBattleSequence as the beginning and/or finale. If you aim for shorter story, try EasilyThwartedAlienInvasion. Remember that in such conflict, humans will have HomeFieldAdvantage. At some point, however, they might feel like they're fighting a HopelessWar. If USA is part of your story, then of course it'll turn into InvadedStatesOfAmerica. Unless you set your story in the countryside, much of it will be UrbanWarfare. Humanity's first line of defense from invader from above are likely to be fighter planes, so be sure to include FighterLaunchingSequence. SensorSuspense works both in air and on the ground. For extra awesome points you can have EpicShipOnShipAction, OldSchoolDogfighting and EpicTankOnTankAction between human and alien tech.

Aliens are probably going to use make use of their higher ground (air?) and so use OrbitalBombardment. You need to shock your readers and underscore the danger - MonumentalDamage and ShockingDefeatLegacy are your friends, as is CurbStompBattle. Soldiers are likely to be NicknamingTheEnemy, so make up something earthly for the aliens.

Your heroes may end up TrappedBehindEnemyLines, adding to the tension. On the other hand, you can go for MilitariesAreUseless and have civilian heroes form LaResistance on alien-occupied territories.

As for the aliens, their appearance depends greatly on the atmosphere you're going for, so take a good long look at first section of AlienTropes and ask yourself what would fit. As to other things, they invade us, so unless you want something more nuanced, AliensAreBastards. If they speak, they may claim TheRightOfASuperiorSpecies. Particularly devious (but also redeemable ones) are AliensSpeakingEnglish, although they may just as well be InscrutableAliens, who are creepier, because NothingIsScarier. Their materials are NotOfThisEarth. BizarreAlienBiology and BizarreAlienPsychology should be in full effect. The rest is covered further in below sections.

If you make your story in more graphic medium, use SpreadingDisasterMapGraphic and BombersOnTheScreen to both cut budget and explain all that's happening without tedious expospeak.

!'''Choices, Choices'''

You'll want to put some thought as to the scope of your story. How many aliens are arriving? Stories have revolved around entire armies (''Film/BattleLosAngeles'') and sole survivors (''Film/ETTheExtraTerrestrial''). Additionally, there's the question of how ''much'' of the invasion you're going to depict. The ''[[Film/RedDawn1984 Red]] [[Film/RedDawn2012 Dawn]]'' films may involve a large-scale invasion of American soil by foreign powers, but mostly focus on one cell of TheResistance, with little news about the rest of the country getting in or out.

What are your aliens like? And, perhaps more pertinently, why are they here? The thing about invasions is that they aren't done for shits and giggles. Basic military strategy: you invade and occupy a region because it has something you want. If aliens are coming here, from godknowshowmany light-years away, it's because there is something valuable on Earth. What is it? Why is it valuable to them? That's going to dictate a lot of things, like their military and occupational strategy, and intersect with the idea of "alien" (IE superior) "technology" in a lot of interesting ways. For instance, if the aliens are PlanetLooters and just here for our water, there's no reason they necessarily have to mount an ''armed'' invasion at all: just park a giant tanker ship in the middle of the ocean and turn on the vacuum hose. The first thing any humans would know about it is when the sea level started dropping, and it would do so in such a gradual fashion that it might take ''years'' for anyone to notice. (Observe how long it's taken us to notice the sea level ''rising'' due to climate change. It's been so gradual that some humans still deny that any such thing is happening.)

What kind of aliens are we talking about? RubberForeheadAliens are played out, but StarfishAliens can be impossible to write. Obviously, you'll want to strike a balance between the two, but what is your exact balance? What is the biology ''of'' these aliens? There are many, many amusing little twists of physiology you could play. Ever messed around with the [[http://en.wikipedia.org/wiki/Chirality_(chemistry) chirality]] of proteins? ''Franchise/MassEffect'' did, to very interesting effect.

A really interesting question: ''when'' is this going to happen? Traditionally these stories fall into the PossibleWar category, taking place in the PresentDay or TwentyMinutesIntoTheFuture (''Literature/EndersGame''), but what about the past? We've already had Film/CowboysAndAliens. How about [[KnightInShiningArmor Knights In Shining Armor]] And Aliens? Cavemen and Aliens? WoodenShipsAndIronMen And Aliens? StandardFantasyRaces And Aliens? Plenty of schlocky action movies, and maybe even some good stories, lie waiting to be discovered here.

There are questions of tone to consider. An Alien Invasion story is science-fiction, which makes it subject to the SlidingScale/MohsScaleOfScienceFictionHardness. How realistic, or at least "consistent with our current understanding of science," do you want your work to be? You don't need to have perfect consistency; ''Film/BattleLosAngeles'' {{handwave}}s most of the tech but has very authentic ''military'' operations, with the invaders utilizing the same sorts of strategies and tactics that humans would in the same situation. Conversely you have ''Film/IndependenceDay'', which was frankly ridiculous on all levels but made a ''lot'' more money.

And there are questions of tone to consider. In RealLife, any alien species that found Earth and decided to mount an offensive operation would probably possess technology [[ClarkesThirdLaw indistinguishable from magic]], and be able to conduct a planet-wide CurbStompBattle with ease. So how ''realistic'' do you want to be? True, there might be an AchillesHeel somewhere in the alien army (say, a thermal exhaust port two meters wide), but how likely is it that the aliens have overlooked it all this time, or that their previous victims never found it? You may need to do some serious juggling to make this work.

Finally, there's the question of whether you need aliens ''at all''. The UrExample of the Alien Invasion story, and one of the precursors of ScienceFiction as a whole, is ''[[https://en.wikipedia.org/wiki/The_Battle_of_Dorking The Battle of Dorking]]'', in which Great Britain is attacked and occupied by technologically-advanced, horrifying StarfishAliens known as... Germans.

!'''Pitfalls'''

The Mohs Scale is a big one here. According to our current understanding of science, FasterThanLightTravel is impossible; there are laws of physics preventing it from occurring. So either you're going to break the laws of physics or you're going to have to put a ''lot'' of planning and preparation into the alien army. Remember how much work it was for Earthers to put a man on the Moon? Well, imagine putting an invading army on a planet which is about a gazillion times further away from us than the Moon is. The monetary expenditure alone would be, well, astronomical. And you'd need to do your absolute damnedest to make sure 1) the soldiers survive the trip, and 2) the soldiers survive the ''fighting'' on the other side, at least long enough to accomplish their mission. Imagine spending $19 trillion on an interstellar mission only to find that the planet's atmosphere is made of magically-anti-''Homo-sapiens'' chemicals and that all the soldiers simply melt upon opening the hatch. Well, as the mission planner (or rather, The Author), it's ''your job'' to imagine those things, and make sure your soldiers don't fall victim to them.

You also need to make sure the whole invasion is for logically plausible reasons. To repeat, an invasion is the military outcome of political or economic desires: "Over there, they have some sort of {{Unobtainium}}, and we want it, and the best way to get it is to take control of the region by swordpoint." An entire period of world history, [[http://en.wikipedia.org/wiki/History_of_colonialism Colonialism]], was driven by this desire, meaning that a lot of modern consumers--or, at least, those who have taken History classes--know something about the hows and whys of what your aliens are trying to do. Make sure their tactics pass muster to those with a high-school education.

!'''Potential Subversions'''

One big subversion is to turn the tables emotionally. One of the advantages of an Alien Invasion story is that the defenders--human beings--almost automatically have the audience on their side, because they (the audience) should be able to see themselves in the defenders. But why ''are'' the invaders invading? And what happens if they lose? ''VideoGame/TalesOfPhantasia'', essentially a fantasy version of an Alien Invasion story, pulled a massive PlotTwist by revealing that the BigBad, Dhaos, had invaded to secure precious resources ({{mana}} specifically), without which his world would wither and die. Though he became a WellIntentionedExtremist along the way (the humans of Phantasia had begun too wreak ecological havoc with {{Magitek}}, and he decided to wipe them out), the heroes acknowledged that defeating him didn't necessarily make them good people, and that they were condemning the citizens of this other world to death by saving their own. (Fortunately, a DeusExMachina helped elevate the emotional tone of the ending.) Most Alien Invasion stories are very clear about the consequences if we humans lose, but what are the consequences if we ''win''?

This leads into the next potential subversion: do military conflicts always have to be solved militarily? Humans have always hoped that it would be possible to coincide peacefully with sentient creatures from other planets, and if these aliens are here for something on Earth, they must have ''something'' similar to us. Maybe peace is possible, if people with calm heads (from both sides of the war) manage to get in contact with each other. Creator/{{Timothy Zahn}}'s ''Literature/TheConquerorsTrilogy'' revolves largely around this, albeit in a SpaceOpera background. You have to be desperate to launch an unprovoked invasion of someone else's homeland, as opposed to the minor military skirmish which starts off the war in ''Conquerors Trilogy''. Of course, this desperation may prove useful when it comes time to hit the negotiating table. Consider taking a brief look at the Creator/OrsonScottCard work ''Literature/SpeakerForTheDead'', sequel to ''Literature/EndersGame'', which doesn't focus a lot on his gay politics and instead talks about InscrutableAliens and the line between them and, well, non-inscrutable aliens.

Yet another subvertion, somewhat stemming from the previous two, is changing the POV of the story. Vast majority of those tales focuses on humans struggling against faceless, inscrutable alien invader. But how about turning the tables and telling the tale of aliens invading yet another planet to add to their empire, only to run into rows of unexpected problems? An alien foot soldier who starts sympathizing with the enemy? Telling the entire story by eyes of alien - especially the one with morality, psychology and/or culture much different than ours - would allow you to refresh a somewhat cliched genre.

!'''Writers' Lounge'''
!!'''Suggested Themes and Aesops'''

There are plenty of {{Green Aesop}}s to be had here. If PlanetLooters are taking the effort to go ga-trillions of miles out of their way and invade our little blue planet, they've probably already wrought ecological hell on their own homeworld. There's definitely an anvil to be dropped there.

Somewhat related to this, you can say that HumansAreBastards, if not [[HumansAreTheRealMonsters the real monsters in this tale]]. You can show that for all that we demonize the alien invaders, they're not acting that much different from the ''conquistadores'' of South and Latin America, or - if you feel like launching yourself into a ''really'' deep political mess - the U.S. in Vietnam. When push comes to shove, we're no different, and the increasingly brutal actions of your characters against the aliens can underscore it.

On the opposite end of the scale, you have what Website/FourChan refers to (slightly mockingly) as ''[[http://1d4chan.org/wiki/Humanity_Fuck_Yeah Humanity, Fuck Yeah]]'' - long story short, humans are ''awesome''. [[HumansAreSpecial We are special]], [[HumansAreWarriors we're warriors]], and most of all, when external threat hits us, we band together and kick the hell out of external threats. With the current trend of darker stories and {{Deconstructor Fleet}}s, this can be a very uplifting aesop.

!!'''Potential Motifs'''

Insect motifs are rather overused in alien stories. Nevertheless, there's a reason they prevail - they scare the audience. Classic elements of those are of course aliens looking like BigCreepyCrawlies, the HiveQueen who doubles as the keystone of aliens' KeystoneArmy and HiveCasteSystem, with soldier-aliens and occasionally glimpsed worker units.

There are many rarer motifs your alien invader could "wear" - demonic appearance, scary masks hinting at {{Proud Warrior Race|Guy}} Culture, avian aliens, reptilian aliens, perhaps even SpaceElves. Given how recently most alien invasion stories has been aiming at something between mammals and insectoids, mostly everything would be a breath of fresh air here.

Aliens can be monolithic, cold entity whose every warrior is identical and which acts according to rules of logic and reasons. If you chose this, go for futuristic, technological feeling and you'll get something along the lines of CyberneticsEatYourSoul. On the other hand, a horde of aliens fighting with techno-swords or better, hand-to-hand-combat, will evoke the fear of primitive barbarism, thus leaning closer towards TheHorde.

From human side, you can go for "humans are awesome", "humans are struggling" or "humans are helpless", which fit in at the most recognizable points of SlidingScaleOfCynicismVersusIdealism. ''Film/IndependenceDay'' is the "awesome" and most idealistic variety. At first, aliens hurt us badly, but when we get our bearings, we proceed to hurt them worse with little actual problems. "Struggling" version, however, sits squarely in the middle of the scale and while humans are capable of fighting back, in this world you need to EarnYourHappyEnding. "Helpless", on the other hand, lends itself for more depressing stories, even though technically it's probably the most realistic realistic. Aliens ''are'' more advanced and the best humans can do against them is to form LaResistance and hope that opportunity to destroy the invaders will present itself.

!!'''Suggested Plots'''

The most basic outline is, of course, that aliens invade the Earth and mankind must defend itself. However, there's a lot of flexibility here. Will your story follow a global defense, jumping from POV to POV in attempt to chronicle a world-wide war? Will you present your readers with only a small piece of a greater tale, showing soldiers warring against the invaders in just one country/region? Or perhaps you're going to show struggles of small, isolated base which has lost contact with the rest of the world and has no idea if anyone but them is fighting anymore? You can also eschew the military completely in favor of showing a group of civillians who try to survive and find sense in the world that has just gone mad.

Another possibility is to set your story ''after'' the invasion. Have mankind won, then, or have they lost? If we lost, then the main focus of the story is usually on LaResistance, but why don't make your hero TheQuisling who aids the invader (now occupier) out of fear, chance at personal gain, or simply because he believes that aliens are better managers than people? If we won, on the other hand, then perhaps we need to find a way to live with survivors of alien army, or we're hunting those survivors down, or maybe we're setting into space to deliver inverted alien invasion to our attackers?

The invasion doesn't have to be global. Perhaps your "invaders" are a bunch of really homicidal aliens which have crashed their ship right outside of some god-forgotten town and decide to raid it to kill everyone. In this case, you should take a good look at HorrorTropes.

A rarely seen option is to focus on diplomats who try to negotiate peace with aliens. This requires a bit more trickery, as there needs to be a reason why species that's attacked as first would now want to negotiate with us. Perhaps there may be dissent among aliens, or even a full-blown ''coup d'etat''.

Something that's pretty much absent as the main plot is humans trying to acquire alien AppliedPhlebotinum. Sure, this happens, but mostly as a sub-plot. How about a story of a spy invading a ship full of HumanAliens to find blueprints for their {{Wave Motion Gun}}s or to blow up their ship while bombs fall on Earth beneath their feet?

And of course, as already mentioned under Subversions, you can write the entire story from alien perspective, shedding a new light on both mankind and invaders themselves.

!'''Departments'''
!!'''Set Designer''' / '''Location Scout'''

Just about anywhere on Earth, when you get down to it. Hell, one crazy filmmaker had his aliens popping out of [[Film/PacificRim the deepest part of the ocean]]!

A bit more to the point, the choice of your location will dictate the tone and atmosphere of your film. Setting it in the city is unsettling, because with all the tall structures blocking our line of sight and sound acting oddly in blocks-created canyons you can never know what awaits you behind the next corner. Ditto for woods and caves, with added bonus that in twentieth century, those are alien surroundings for many of us. On the other hand, setting your story among fields, on great expanse of grass, lends itself nicely to feeling of loneliness, but also means that your characters need to keep constant vigil - if they can see aliens, aliens can see them, too. Yet another option is to put your story on a ship, or in a maze of abandoned skyscraper. In addition to things mentioned about cities and woods, this lets you craft atmosphere of isolation and mounting paranoia, especially if contact with outside is lost.

Go for SceneryGorn - nothing underscores the threat and evilness of aliens like showing cities blown to smithreens or villages slaughtered and burned in the wake of invaders' raiding party. Some gratuitous MonumentalDamage is fine and dandy, but don't overdo it too much - headless Miss Liberty and falling Golden Gate bridge are so cliche many of us would probably be surprised to find the two of them intact in RealLife.

Does your story take place mostly in the light of the day or by night? Day lets you show the danger clearly and is better in more idealistic and optimistic tales. On the other hand, night underscores danger, uncertainity and isolation, thus giving you more narrative tension. Then again, you can make readers bite their nails even when sun is shining bright.

!!'''Props Department'''

This is where you can let your imagination run wild. What do the aliens use? Do they fly in a classic FlyingSaucer, or a more menacing triangle? Do they use [[RayGun ray guns]], or do they still have [[KineticWeaponsAreJustBetter projectile weapons]]? Do they require space suits in our atmosphere, or not? Also, be sure to have the tech be consistent. It may not make too much sense for aliens whose technology is mostly [[OrganicTechnology organic]] to have huge metallic [[MasterComputer super computers]].

Remember, also, to fit the weapons and spaceships to your aliens. If the creatures are three- or four-handed, have their heavy guns need all hands to work. If your aliens are quadrupedal, don't have their spaceships' cockpits be fitted with human-style armchairs. If they're blind, they don't need translucent windows, or any windows, for that matter. Think what would make sense from ''their'' perspective, not ours.

As for humans, go for real-life military technology. Make fighters engage spaceships, match heavy sniper guns against aliens' futuristic guns. Apart from that, however, remember about weaponry not often seen in alien invasion movies. Imagine tanks engaging large alien structures and keep nuclear submarines in mind.

!!'''Costume Designer'''

For aliens: any armor or spacesuit they might require. If you go for more savage type, make them wear no armor and have unnaturally strong natural hides, or perhaps armor that looks like it's part of them. The higher on apparent tech level ladder the aliens climb, the more sci-fi-ey the armor will look. The ones in the middle of the scale might have bulky and heavy PowerArmor. The highest ones might go for something that's close to their skin, yet provides protection. Go for sharp edges and flat surfaces rarther than curved, spherical shapes which make it look as if child safety specialist or Apple salesman has just finished inspecting the invasion fleet.

As to aliens' masks, today most go for FacelessGoons approach, where all enemies look identical. You can take this in many different ways - perhaps they're {{The Blank}}s, or maybe there's some humanlike, yet [[RageHelm foreboding]] or {{Uncanny Valley}}ish quality to them. On the other hand, if you're feeling creative, make each mask different. Why? Perhaps it denotes the clan this particular warrior comes from, or calls for favor to aliens' chosen god, or maybe aliens are painting their masks for quick identification on the battlefield, or just to stand out. Going beyond FacelessGoons can flesh out your aliens' culture. On the other hand, if your aliens have terrifying faces by themselves, you can throw helmets away completely and scare your humans with mandibles or MoreTeethThanTheOsmondFamily.

For humans: whatever fits with the time period, really. Camos and military grab for soldiers, civilian clothing for non-soldiers, lab coats for scientists. Keep it reasonable - running from alien threats in miniskirt and high heels might be {{Fanservice}} incarnate, but not only does it look awkward, it's likely to end up with MsFanservice falling over, or freezing, or getting hurt in unprotected parts of her body. It's like they tell you in real life - dress sensibly and appropriately to occasion.

!!'''Casting Director'''

TheEveryman is often a good protagonist, just someone who ends up getting caught up in the global devastations. Your usual reader or viewer has the highest chance to sympathise with character like this and see himself in him. If you decide on this archetype, he's unlikely to be a badass who takes aliens down with rocket launchers and hand-to-hand comabt - more along the lines of ActionSurvivor. This also limits the scope of your work, but if you don't want to focus on military operations and global scale, that's the right man for you.

Military types get to enjoy more action in those types of settings. They're our first line of defense against any invader, after all. They're unlikely to be lone wolves, too - TheSquad is necessary. They will see the most action, they will know the high commands' plans... and they'll quite probably be surrounded by scores of {{Red Shirt}}s dying by droves. The thing to consider is also that their training makes them unnaturally calm when faced with combat or devastation, which may make it hard for reader to identify with them. Nevertheless, if you want to take fight to the enemy in professional manner, this is your guy.

ScienceHero is usually a member of supporting cast rather than the main character. Him and his lab-mates are working on cracking the secrets of BizarreAlienBiology and how to turn it against the invaders. He's the one to sprout TechnoBabble and provide the story with AppliedPhlebotinum or more down-to-eath method of taking down the invaders. He's also the one to function as MrExposition, speculating on alien origins, setting down the rules of the 'verse for the readers and provide MissionControl. If you want to focus on "why" rather than "how" or you prefer more though-out approach to fending hordes of aliens, this character is for you.

Finally, don't forget CharacterDevelopment. Any character can start out as one of these archetypes; that doesn't mean they have to end the story that way. One of the (few) storytelling beats the Creator/MichaelBay Film/TransformersFilmSeries did a good job on was chronicling the gradual evolution of Sam Witwicky (Creator/ShiaLaBeouf) from helpless, have-to-run-away-from-everything (I-mean-holy-shit-they're-100-foot-tall-robots) ActionSurvivor in the first film to, in the third, BadassNormal who can DavidVersusGoliath a Decepticon and win.

As for the aliens, this has been discussed in depth in above sections, especially Choices and Motifs. For additional clues, you may want to take a look at SoYouWantTo/CreateBelievableAliens and SoYouWantTo/DesignAnAlienMind. Whatever you settle for, just remember that your aliens come from very martial, very genocidal, very full-of-themselves or very desperate culture, otherwise your plot just plain wouldn't happen.

!!'''Stunt Department'''

Scenes of global destruction are a staple of alien invasion stories. Cities are ravaged and destroyed to any point between smoking, holey skyscrapers and large crater where a sprawling metropolises used to be. MonumentalDamage abounds. Planes and fighters fall out of the sky like flies and people and places are strafed.

Closer to the ground, you can show your aliens mowing down soldiers, civilians or both. In fight, humans will likely make use of as much cover as is available, while aliens either No Sell them and just go through the bullets or use cover themselves. In hand-to-hand, it's nice to show humans as somewhat inferior in terms of strength. Show aliens smacking them around a few times like it's nothing. Have humans be the GuileHero to aliens' TheBrute.

Out of combat, have your characters play deadly hide-and-seek with aliens, trying to sneak by the enemy they have no chance to match. Those are scenes that work the best at night and if done correctly, they can be more nerve-wrecking and memorable than a dozen shootouts.

Oh, and remember to include lots of StuffBlowingUp. People love that.

!'''Extra Credit'''
!!'''The Greats'''

As [[Film/TheWizardOfOz someone once said]], it's always best to start at the beginning. H.G. Wells' ''Literature/TheWarOfTheWorlds'' is the founding work of the genre. Its two main film adaptations, ''Film/TheWarOfTheWorlds1953'' and ''Film/WarOfTheWorlds2005'', both explore different aspects of the invasion, the former focusing on the broad global invasion and the latter on a single family's struggle to survive.

For an invasion based on subterfuge, Jack Finney's ''[[Film/InvasionOfTheBodySnatchers The Body Snatchers]]'' is a great work which explores paranoia and loss of identity, as do its 1956 and 1978 film adaptations.

!!'''The Epic Fails'''

Make sure that the aliens invade for logical reasons. One of the recurring criticism’s of ''{{Film/Signs}}'' is that the aliens are allergic to water, and yet they invade a planet mostly covered in water with high amounts of precipitation while ''[[TooDumbToLive walking around completely unarmed]]''. Also, try to ensure that your characters are likable. The latter two adaptations of ''Body Snatchers'' make the characters so unlikable that you may cheer for the pod people to win.

For another variety of a fail, a good lesson on importance of {{Foreshadowing}} and keeping to your rules in story is ''Literature/OutOfTheDark''. While a SoOkayItsAverage book overally, a combination of UnexpectedGenreChange and really good RedHerring resulted in a TwistEnding DeusExMachina of epic proportions. Read it, if only to see what went wrong.
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