What are some tactics for the ancient Greeks to defeat alien invaders?

Question

Context

It's the 4th century BC, Alexander the Great has just passed away and his empire has been divided amongst his generals. Now the successor states of Egypt, the Seleucid Empire, Macedonia, Bactria and others have inherited his legacy and stand on strong military grounds.

However, rather than begin fighting themselves, in this story, aliens from a distant world have landed in (let’s say) Syria and have begun a conquest of the world. The Greek successor empires have decided to form a united league to defeat them.

The aliens, however, have limited resources as they were attempting to escape a dying world. They are a humanoid race but rely on technology and machinery to do most of their work. They number around 15,000 and use a type of automatic projectile weapon that can be equated to an AK-47.

The Question

The Seleucids, Egyptians and other successor kingdoms are able to defend themselves quite well against other human civilisations. They employ professional armies (hoplites, pikemen, cavalry, archers), mercenaries, siege craft, elephants and also native conscripts.

How can they defend themselves and eventually defeat the invaders?

Assumptions

• These aliens can survive on Earth. They need food and water.
• Their ammunition and fuel is limited but initially plentiful.
• They have no aircraft (they crash landed) but possess around 100 ground vehicles that we can equate to tanks.
• The Greek empires possess leaders with strong military backgrounds and experience.
• The aliens are seeking conquest to rule all humans.
• The aliens can be diplomatic.

EDIT: further assumptions based on commenters questions:

• breeding process is similar to humans.
• forcing the aliens into submission OR total annihilation is what I mean by defeat

Answer 1

Victory through arms

Without advanced sensing equipment, the aliens are vulnerable to ambush. Battles on an open plain, with both sides lined up, will be won overwhelmingly by the aliens. Battles fought in forests, jungles, or hills, or at night, will allow the humans to surprise the aliens and have at least a fair fight. If the defenders are particularly stubborn, house-to-house fighting in cities gives the locals plenty of opportunities to ambush small groups of aliens.

If the aliens want to move safely, they're going to have to move in large groups. But if they're moving in large groups, then they're probably leaving some places undefended – various bits of infrastructure, like supply depots, caravans, observation posts, and minor administrative centers, will be easy pickings for a sufficiently-motivated group of humans. 15,000 aliens just isn't enough people to guard all of the things the aliens need to survive and expand their empire. And as the empire gets bigger, there are more things to guard. In the long run, the humans should be able to pick off the aliens in small groups. Since the aliens can't replace anyone who dies, while the humans have a large supply of able-bodied males to use as replacements, it will be a long-running battle of attrition with the humans as the eventual victors. Victory: humans, eventually.

Victory through diplomacy

On the other hand, since the aliens are going to have overwhelming force at first, they're going to be able to completely overawe the first new nations of humans they meet. The first general that brings a sword to a gunfight is going to have his army destroyed. Depending on how bad the defeat is, and the political situation, the defending king might surrender and offer to be a client state. At this point, the aliens now control an army of local humans, which they can use against the other local humans. If the aliens can repeat this result often enough, then they'll control enough kingdoms and armies to be able to (eventually) take over the world.

Except... no matter how you slice it, there are still too many humans. And there's always some ambitious punk who thinks that he should be in charge, and can collect a few (thousand) friends who agree with him. With each revolt, some aliens will be killed – maybe a few, maybe an entire enclave if the revolt can ambush them. The alien numbers will dwindle, until eventually there aren't enough of them left to stop a frontal assault. Victory: humans, eventually.

Victory through treachery

This is an extension of the diplomacy victory above. If a kingdom surrenders, then the humans within it retain some amount of power – there are going to be human administrators, human police, and human laborers working to further the aliens' goals. Those human administrators will have the power to make local decisions regarding the police and laborers. Sooner or later, you're going to get a "trusted" human who decides that he's tired of this alien overlord nonsense and stabs the lot of them in the back.

Answer 2

I simply do not believe that human race has a chance in your scenario.

The difference in technological advancement is too huge. We are speaking about a small group of people who were able to build a space ship which was able to transport them from a distant star against people who will wait for 1000 years to be able to use gunpowder. I will try to explain my reasoning in the bullet points below.

• People in other answers claimed that the army would be overwhelmed with 300 mln people, but based on this source it was ~ 160mln. This sounds like a lot but all these people are spread around many continents, speak a huge variety of different languages and have no reliable and fast way of communicating with each other. It would take them years to reach some particular destination (and even if they will reach it, two armies would not be able to agree what to do due to the language barrier). Also do not forget that army is a really costly toy. You need to feed, pay, and sustain them. Look at the numbers: one of the biggest armies in the world Chinese Red Liberation army had 2.2 million people and was 0.18% of country population (which worked like hell to sustain it). If you multiply the total population even by 0.18% you suddenly end up with less than 0.3 mln.
• I think we can not compare the Korean War to this war. First of all the technological gap was not so significant and USSR/China who supplied weapons to North Korea diminished this gap even further. Also there is a big difference between a kill them all war and a war where you try to show to your country and to all other countries that you are not killing civilians and unarmed people. Based on this our situation, aliens do not care whom, how and how many people would they kill.
• People are talking about mass poisoning of water forget about what era are we talking about. Remember, the first successful mass poisoning (I am not speaking here about killing of one/few people with treason) happened during World War One on Marne river and was considered really inventive. So yeah, let's wait for a couple of thousand of years to attempt to poison an army whose technological advance would allow to detect this poison from a distance of a few kilometers.
• Outmaneuver an army? With what? With people carrying tens of kilos of armor? Or with a horse with an average speed of 30 miles/hour (without armor and weapons)? All of this against a tank which easily achieves 30 miles/hour and kills from a distance of 2.5 km even right now, so what should we expect from the tanks of a civilization which was able to create spaceships?
• Vulnerable to ambush. Maybe, but for some reason I believe that aliens have heard about infrared lights and radio. Also why would they try to conquer a forest? Their goal is to take strategic places and not try to clear everything from people.
• Diplomacy and kingdoms of humankind working together to defeat aliens. Sounds really good, but how many war-free years has there been during the reign of humans? Not a lot. So why do we think that an Egyptian civilization would not want to be the chosen nation of their Gods, who heard their prayers and came to help them to conquer the world? If not Egyptian then any other empire. Remember that aliens are really smart and most probably their civilization has seen way more wars to learn from about diplomacy and war conflicts.

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So basically ancient civilizations have 0 chance.

Germany invaded Poland in one month (Poland had a normal army during that time) it took 3 days for the allies to decide what to do and even after they declared a war, they had done absolutely nothing. What do you think, how much time would it take our ancient civilizations to figure out that some other civilization far far away was destroyed. Would they care? How fast would they decide to do anything?

Technology was always a huge advantage. Just a small advance (who created the first tank, built the radar, broke encryption, developed an atomic bomb, created a catapult) was frequently causing a decisive win.

A lot of our technological things are not really hard to replicate. A person like me can create a molotov cocktail, create an explosion and make a radio. Can you imagine what a university chemistry student can create in a day? What could a group of specially trained and prepared people do? Every one week that the ancient army is waiting, aliens can replicate some of their old inventions.

Aliens do not need to kill everyone, nor they will come to Earth and broadcast to every civilization - "Prepare, we came to kill you all". They are smart and they came at a time, when everyone believes in Gods and the ones that do not believe, should be killed in sacred ritual to please the aforementioned Gods. So why not to pretend to be the same Gods, use some civilization as slaves (giving them some cool toys) and quickly try to replicate inventions. Before you speak about how hard it is to control a big population, that there will be revolts and other stuff like this, check how many German people died when there were only very limited amount of them in occupied France and Poland, also check how many people were needed to overview huge concentration camps and how many jews tried to make a revolt.

Answer 3

Without resupply or reinforcement, I think the aliens would be overwhelmed... eventually...

The numbers tell the story.

Earth's human population at that time is estimated at about 300 million, granted many of those humans were living in east Asia, but with just a few million soldiers overwhelming a force of 15 thousand would be doable.

It would likely cost a ridiculous number of human lives, but with numbers that slanted an ongoing siege would eventually wear down the aliens' ammunition, fuel, and so on...

There are similar stories about slanted battles during the Korean War. Supposedly well fortified and well armed US forces were overrun by poorly armed North Korean forces, just by the sheer numbers. Basically wave after wave of troops were ordered to charge into machine gun fire until ammunition ran low and the ground was taken.

See: Human Wave Attack and Attrition Warfare

Answer 4

Defeat aliens with least loss of human soldiers.

Reach upstream and Poison the flowing water source, also heavily poison underground water from some distance (diffusion will mix the poison into alien's underground water).

Ancients were good with poisons just need to mass produce them. Putting lots of mud, dead rotten animals, cobra snake poison, feces (with pathogens) etc are the few options.

That will keep them moving (with limited fuel and stamina).

Avoid direct confrontation. If they chase, then run. Remain scattered.

Have multiple supply lines. Destroy all unprotected fields or trees on the circumference. Wait for harsh weather season. Just like Russian scorched earth and waiting for winter.

When they start dying of hunger. Ask them to surrender their arms in exchange of constant food supply and water.

Answer 5

Just because the aliens are the ones with the guns now doesn't mean that humanity can't acquire them. If the aliens possess no unarmed physical or mental advantages over the humans, the humans should be able to engineer some way to ambush a patrol, pilfer a depot, or otherwise procure some firepower of their own. It might take awhile to shift a meaningful amount of technology into their own hands, but once they get a little of it, acquiring more becomes easier.

Pick off any small patrols, take their stuff. Once sufficient stuff acquired, raid enemy encampments. Eventually win with overwhelming numbers.

Answer 6

This event did, in fact, happen.

Almost 500 years ago in Central America, very strange and weird-looking people showed up coming from beyond the endless waters which the locals had no technology to cross. They had strange and powerful, almost magic-like weapons. Cortes had less then a thousand soldiers, but in the end managed to conquer a whole empire.

No matter how powerful and fearsome their weapons were, a few hundred men would have had no chance of conquering a whole empire. So how did they manage to do it? The Aztec Empire was brutally oppressing a lot of different tribes, and those tribes decided that they would rather live under Spanish rule than being used as human sacrifices in the Aztec rituals. This is how, when Cortes conquered the Aztec capital, he didn't do it only with his original few hundred men. He had almost 100000 native allies under his command. The Spanish not just managed to temporarily defeat a much more numerous force, but managed to settle down, and the region is now dominated by Spanish culture even 500 years later.

The technology of the Aztecs was not much better or worse than the technology of ancient Greece, and the Conquistadors were fewer than 15000 and had less advanced technology than the aliens in the question.

So, if the aliens in the question behaved similarly, they could have a very good chance of building a country or an empire for themselves. Instead of mindlessly starting to gun down humans, they could trade with them, then find a very oppressive satrap and convince humans to help the aliens overthrow him. If done right, many humans would see them as liberators, rather than conquerors. Cortes also didn't jump out of his ship while opening fire on the natives on the shore. He wasn't even explicitly sent to conquer, just to explore, trade, and look for opportunities. He found a crumbling empire with a lot of enemies, and he saw it as a very good opportunity.

The question asked how the Greeks could defeat the aliens. However, if the aliens were at least as smart as Cortes, then the Greeks would have no opportunity to defeat the aliens, as there would be no united Greek force fighting against them.

Answer 7

When I read this question, the first thing that came to mind was the Comanche tribe of Native Americans. Throughout the 18th and 19th centuries, the Comanche fought against settlers encroaching on their lands (the southern part of the North American Great Plains). The Comanche war bands weren't very far past a stone age level, using arrows and lances fashioned using primitive hand tools. The foes they were fighting had pistols and rifles, built fortified bases, and had formal military training. Despite this large technological gap (roughly similar to what the OP is going for), the Comanche were able to successfully hold their own against a significantly more advanced foe for a very long period of time. Your ancient people can use similar tactics and methods to fight off their technologically-superior invaders. (for more details on Comanche warfare, see the excellent book Empire of the Summer Moon)

Comanches swarmed their enemies. One on one, superior firepower usually wins. Comanches attacked in groups and on horseback, and opponents had a hard time tracking so many fast-moving foes that were all moving independently. The psychological impacts of being vastly outnumbered should also not be ignored. The alien population numbers that you give are low enough that swarm warfare could be an effective tactic.

The Comanche protected themselves from gunfire using shields. Several layers of dried, tanned buffalo hide was capable of stopping a rifle shot. Even though an AK-47 round is more deadly than a 1850's rifle slug, it's plausible that an ancient civilization could develop a type of shield capable of either stopping oncoming gunfire, or at least rendering it non-lethal. The American TV show Mythbusters has done lots of experiments testing whether common objects are bulletproof, and they've shown that objects made of materials available to the ancient Greeks (ceramic, nickel, etc) were capable of stopping certain modern bullets, or at least robbing them of enough momentum to make them survivable. Layering materials like nickel and dense hides could result in a shield capable of protecting against a modern automatic rifle (provided that you're not subjecting it to sustained, focused fire). It may be heavy enough to require a dedicated shield-bearer, but I believe that was already used as a military tactic during that time period.

The Comanche also had a large advantage by being masters of horsemanship. Horses provided unmatched speed, stamina, and maneuverability in their world. Even in your world, a well-coordinated and well-trained mounted cavalry can be a threat to armored military vehicles. A tank can match a horse in speed, but not in agility. Tanks are great against massed or fortified enemies, but much less efficient at attacking a swarm of enemies that are spread out, surrounding it, and constantly moving. An agile cavalry can cause tanks to catch each other in crossfire, or deliver soldiers close enough to jump from the horse onto the tank and attack it directly. Tanks are stopped/slowed by terrain that a cavalry can successfully navigate (narrow passes, forests, etc), and even a primitive civilization can create traps to defend against tanks (such as moats or tiger traps).

Also, remember that even the ancient Greeks had access to what is still one of the most destructive weapons available: fire. Unless your aliens have advanced to the point where everything they use is metal or plastic, fire is still a real threat. A small group of soldiers making it into an alien building with torches can easily start a fire capable of destroying most of a base. Several ancient civilizations were known to use early forms of incendiary weapons, so this isn't too far from reality. Your example listed the aliens landing in Syria - a region not known for having plentiful water - which would increase the danger posed by an army of arsonists.

Any sort of a war like this would revolve around attrition. The aliens have no reinforcements and a finite level of supplies. Once they run out of certain key supplies like fuel and ammunition, it's unlikely that they'll be able to manufacture more (at least not in any real quantity). At that point, they face many of the same problems that a modern army would face if time-warped two millennia into the past. They're stuck with none of the modern trappings that they've been accustomed to for their entire life. At this point, survival is difficult even if you completely take away any sort of military threat. The aliens would have no modern medicine, little (if any) knowledge of Earth's plants and animals, no familiarity with the local geography or weather, and would likely not know how to build tools or buildings from complete scratch. If the local people could force the aliens to burn through enough of their consumable supplies, a good, old-fashioned siege could be very effective.

Answer 8

Well, you put up some big problems for the aliens. Small resources, small numbers and very restricted technology - believing that Aliens that can cross the space to reach humans can only offer automatic projectile weapons and tanks as offensive potential is somewhat difficult.

But anyways - as the humans not prepared for this, the aliens at first will have an edge. Wherever they land they are probably able to destroy the leadership and establish themselfes as new leaders with their advanced weaponry. So they can rule humans in that region to supply them with food and other resources.

But growing over the size of an country can be difficult, as they have so few vehicles and few numbers. The neighboring countries will be better prepared, so while the humans still will need some time to figure out stuff, the problems of controlling big numbers of people and a big area with only 15.000 are too large. If the aliens try to destroy humanity they are stupid, ruling them to get resources through them is much more clever.

Some tactics the other countries may develop: avoid direct confrontation, but attack supply lines (attack the food delivery for instance) and separated smaller groups of aliens. Loot some of their weapons. Obstruct paths so that the vehicles cannot move. Use ambushes to attack and retreat fast after first attack. They may develop shields that can stop bullets, although they are probably heavy. The aliens probably can be stopped.

Really clever aliens would not go to war but establish themself as traders, hich-tech-products are exchanged for food and resources. Local rulers that benefit from that trade would even start to defend the aliens from other people.

Answer 9

Automatic weapons FTW. Humans lose. Game over.

You want examples, look at European colonisation. Rorke's Drift for a classic example. Isandlwana was a win for the Zulus only because the British were poorly equipped and weren't seriously prepared for resistance. And that's with 19th century technology - replace those old carbines with something equivalent to modern assault rifles, and the result would be a foregone conclusion.

If you look at Darius's campaign, you'd be lucky to get half a million troops in one place. More typically you'd be looking at maybe 100,000 tops on the one battlefiled. Up against 15,000 guys with assault rifles, they're dead meat.

You're also starting from a false assumption of "rule all humans". If European colonisation taught us anything, it's that ruling the locals is never the point; it's ruling the land and having your people take its resources for themselves. The locals might be kept on suffrage, or for a slave workforce if you're short on manpower, but more usually they'll be massacred. There's no benefit for the aliens in keeping humans alive.

The other false assumption is "limited fuel and ammunition". Once they have a well-defended beachhead (which won't take long with automatic weapons), the first priority is resupply. Worlds don't die overnight - these guys had plenty enough time to make sure their colony ship had refining/manufacturing facilities, or at least the means to build them when they land.

Answer 10

For reference, you probably should take note of some things about where we ourselves are at in terms of conceivably being in the position of the aliens, both technologically and politically.

Perhaps the most important issue is that engineers who have proposed colonizing other planets always start out making industrialization a top priority because fulfilling all of our needs depends on having resources provided by industries of some kind. This includes getting food and water, resupplying, and building shelters and equipment, all starting from raw materials, meaning whatever stuff just happens to be laying around. You could say that these engineers are so obsessed with industrialization that they have already been playing with the idea of sending 3D printers to the International Space Station to produce replacement machine parts and such there, thus reducing the need for resupplying missions. The aliens in this story would undoubtably have the same kinds of priorities. Additionally, many if not most of the materials that these aliens would be likely to want (e.g. iron, silicon, copper, aluminum, and carbon) are fairly easy to find on Earth. They could probably produce still other materials (e.g. "rare Earth" metals) through nuclear fusion using their technology. We can then figure that they would immediately get busy manufacturing stuff upon landing on Earth and would not take too long to fix the problem of supply and equipment shortages.

Chances are pretty good that if they have developed the technology needed to travel to faraway stars they have also figured out how to make the power and propulsion systems needed to make all sorts of stuff fly around. We ourselves are more or less nearing that kind of milestone with drones and VTOL aircraft. The tanks that these aliens have would therefore probably be aircraft if not full-fledged spacecraft, and they would not bother much with operating as ground vehicles because of the obsolescence of that mode of operation. Moreover, arrows and spears would do nothing to these tanks, these tanks would be able to fire rapidly and blow things up to take out large numbers of foes quickly, and their speed would enable them to pretty much go and be anywhere at any time as needed. Nukes and similarly destructive weapons (including "spear from God" kinetic weapons) would probably be fairly easy for them to make too, so if they wanted to, they could level whole enemy settlements with one shot.

However, we can also imagine that in their home planet, military technology would have caused the extinction of these aliens if not for them being peaceful and empathetic by nature. We can then assume that they prefer to be peaceful and let others live. Thus, even though they would likely be able to wipe out all their human enemies without much effort, things would get sticky and unpredictable as a result of moral dilemas and then very tricky and complicated politics. For example, should the aliens turn Earth into a colony, try to teach humans to become more civilized and sophisticated, and try to coexist, turning the resulting civilization into some kind of melting pot? Inevitably, there would be political conflicts because of vested interests among high-ranking humans, people being hostile to changes in their ways of life, people perceiving counter-cultural forces as being evil and just plain wrong, and the aliens becoming entangled in humanity's pre-existing political and ideological conflicts. The aliens too would certainly find themselves wrestling with the question of what to do about primitive practices concerning alleged crimes and punishment in much the same way that the U.S. military has been wrestling over this against the Taliban in Afghanistan with regard to women's equality, human trafficking, and standards for justice and punishment. After throwing in the colossal technological and cultural gap, that conflict is where this story would get very interesting.

Answer 11

I see where you are going, but i'm trying to find a way to make the "war" happen.

The first thing i'm wondering about is in both Egyptian, Roman and Greek mythology the gods came from heaven. And in times where religion was the thing to hang on to, i think most people would assume they were gods (kind of like the STAR GÅTE thing)

For the war to happen there would have to be some reliable person say priest or the like who starts to claim that they have to be false gods. Or the uneducated would just assume that the gods came back to claim their rights and the commoners would submit wiht out any resistance

Answer 12

The aliens are in a fairly desperate position: There is not many of them, they have no infrastructure, they have little knowledge about the planet and it's inhabitants, and most of all there are not very many of them.

But they are technologically advanced in ways that must seem more than magic to the humans.

While they have limited supply aof ammunitions, they should have no problem at all to simply build some really strong crossbows as soon as their ammunition supplies start to wear out.

So, over time, they will conquer the world, and they will not have too many problems with that.

Unless...

Unless they are beaten hard and fast. At the beginning, they will be quite busy creating some infrastructure. That is the time when they are fairly weak: They will have little fortifications, not very well established food and water supply, and little knowledge about the humans' abilities. This should be the time to strike at as many fronts as possible: hinder their access to water and food, and try to mass attack them as hard as possible.

The losses on the side of the humans will be enormous, but there are many of them. They will need to learn about covert actions, because simply marching up at the aliens in square formation will get them killed.

But we can assume that their generals will learn.

They will try to use the terrain to their advantage, use shields to at least obscure the line of sight for alien snipers, use ranged weapons as well as fire, use ambushes and traps, to diminuish the alien forces as good as possible, trying not to allow them time to reorganize, and most of all, no time to replenish their food reserves or fortify their positions.

If the human generals fail at this, the aliens win, no matter what.

Answer 13

The middle eastern world in the 4th century was run by decentralized empires who didn't control their people or land directly: they used satraps (subordinate kings) to do the daily administration of the greater empire. Alexander the Great and the earlier Persian rulers styled themselves "king of kings" who let the local rulers keep control of their regions while collecting taxes in gold, goods, soldiers, and labor from them. There is no reason that the aliens couldn't sweep across the ancient world making subjects out the other empires instead of destroying them, just like Alexander did. The Greeks and other peoples would understand this kind of hands off government and the aliens would benefit from not having to personally administer a huge swath of land and people. The aliens could slot themselves right into the order of things as the new overlords and watch the gold roll in from their human subjects, giving tech and protection to their satraps in return for loyalty.

Answer 14

One problem most answers have is that a civilization which is capable of interstellar travel is significantly more advanced than the technologies you describe as being available. A solution is that the technology they used to travel, escaping their world, is not their own. I'll leave it to you to decide how they discover & use it. Then you can arbitrarily set the level of technology available to them.

On arrival the aliens will see the relative technology level and will either act arrogantly or cautiously depending on their culture and leadership. If they act cautiously then they will overwhelm a technologically inferior species, through diplomacy/tactics (see other answers where aliens win). However if they are arrogant, then they will announce their arrival and show their intent which will give many opportunities for the natives to set up this 'league' and for religion to view them negatively.

As for the war itself, most decisions come down to the leadership of this league and it's structure. If it acts cautiously, measures it's foe without over committing, using scouting etc. It has the opportunity to develop new tactics. Without this, they will attempt pitched battle which will almost inevitably be a loss and any further resistance will be hampered by fear and lost resources, both the army and useful individuals within it.

Other points I've thought of.

• How do the natives deal with 'traitor nations/cities'?
• Can the natives learn to use the alien technology?
• Logistics, what proportion of motorized transport does the alien race have, do they still have to rely on foot/carts to transport resources/supplies?

Answer 15

I believe it will be more war of wits rather than arms.

In open fight, earthling does not have any chance to win. Tanks will decimate entire army, then few soldiers with hand weapons will execute rest of defenders.

Only chance for Greeks is guerrilla warfare. Surprised attack on small units, stealing their equipment, sneaking to their camps and slicing their throats. Poison their supplies.

Another option will be let aliens win, learn what their civilization can offer us, and then backstab them.

Answer 16

David Drake has written a variety of stories set in ancient times with an encounter of an alien agent or critter setting up to take over the world. Birds of Prey is one, Killer is another. Several short stories have this aspect.

An equalizer here is that the aliens are infiltrating Rome alone, or nearly so and can't get into a pitched battle with high tech. They use it to gain street cred as magicians, which gives the counter-agent ways to get close enough for a sword blow. In Birds of Prey there is a second alien agent setting up the mission to eradicate a brood of alien eggs watched over by an armed brood mother with an electrical gun - they modify parade armor to conduct the charge away long enough for a sword attack.

Answer 17

An interesting fact about having a technology edge in war is that sooner or latter the other side is going to figure out how your toys work and use them against you.

If humanity is going to win, it going to be victory based in wit, understanding the enemy and using there own strength against them. You likely want a trickster hero and a nice opening battle where the alien's curb stomp a huge human army... you know to set tone and show how one sided a straight up fight with them would be.

I also be tempted to give the alien's background some thought, maybe they have limited supplies and support because something bad happened to them (crashed ship maybe?), perhaps there even a way the story might end well for both factions as well.

Answer 18

The aliens do not have a chance.

Some assumptions: The alien race is roughly human in their behaviour and didn't have advanced knowledge of their destination before they left.

So who will be amongst those 15,000? Some carefully chosen groups that contains all the necessary skills to rebuild? That's just not human (or alien) nature. The 15,000 people would represent those with sufficient security clearance from a single nation/tribe. Additionally, those who were truly needed would also be able to score an invite for their family.

So we would end up with maybe 2000 soldiers, 1000 scientists/engineers, 1000 politicians and billionaires, as well as around 11,000 people with no particular reason to be there but with a connection to one of the above groups.

So we have 2000 soldiers to guard against the entire of humanity. These are spread into 3 groups of under 700: Guarding mines scattered around the world, guarding the city and farms, and destroying humanity. All the tanks would be parked outside of the alien Capitol and left alone or partially dismantled - too much fuel consumption to use and risk of humans stealing them if they aren't carefully disabled.

The first targets would be the invading army and those guarding the mines. If their technology is broadly comparable to modern humanity, they need iron, a fossil fuel like coal or oil, and ingredients for gunpowder. So lets assume they build 3 mines total. At all times, they need to guard these 3 mines or the humans will use or destroy them, and they need a mobile force capable of taking the mined goods to the city. So divide out 667 mine guards into 4 groups and we get groups of 167.

I don't care that they have machine guns, 167 people cannot fight an ambush from a 4th century army.

So humanity opens by obliterating 167 aliens, potentially losing tens of thousands of men in the process.

But now, they have 167 of the guns. At that point, the aliens are dead. They are outnumbered thousands to 1, need to divide into even smaller groups to create a new group to collect goods from the mines, and the humans have advanced weaponry.

A similar approach could be taken with the invading alien army. They will need supply lines. Attack the supply lines to gain weapons, then use them to destroy the army.

Answer 19

The Element of Surprise

I think the only way the Greeks could defeat an arguably superior enemy is through tactics that take the aliens by surprise.

Flanking - this pits an unfortunate few against your aliens in the field, while the bulk of your army is in the trees (or whatever) to the left, right, and back of your enemy. This maneuver was used by the Greeks in the Battle of Marathon.

Traps - The classical use of the trou de loup would trap and kill approaching enemies. Simply make your pit large enough to sufficiently trap your odd alien or two.

Guerrilla Warfare - an out-powered defensive military can use the tactics explained by Sun Tzu in The Art of War as early as the second century BC.

"All warfare is based on deception. Hence, when we are able to attack, we must seem unable; when using our forces, we must appear inactive; when we are near, we must make the enemy believe we are far away; when far away, we must make him believe we are near." -- Sun Tzu

Answer 20

Several of the other answers have made good arguments for why -4th century humans with -4th century technology would have no chance against an invasion by an advanced, spacefaring civilization.

But what if the humans were somehow able to gain access to the aliens' own technology, and use it against them? For example, a schism in the alien society results in a small alien faction attempting to gain dominance by arming and training human mercenaries.

Or, some clever humans could manage to steal some of the technology. In this case, they'd have to steal enough weapons to make an impact, as the manufacturing infrastructure would not be there for humans to build their own AK-47s.

But in any case, with access to alien technology and a large population to draw conscripts from, I'd imagine Alexander's generals could stand a pretty good chance.

Answer 21

Normally, when you have such big advantages and disadvantages, even if each side has both, the conflict doesn't last long. One side or another is taken out pretty quickly (generally in a single day's battle) being that both side's holds on power are so unstable. This kind of story could perhaps work for an action movie, but it wouldn't be all that interesting simply because the story would end far too quickly. Also, if primitive humans take out the aliens simply through attrition, outnumbering them during an attack, that too would not leave much room for variety in the plot. A good plot calls for the winning side using a clever strategy, but a strategy of mere attrition would make things a bit too predictable and monotonous. It would just turn into a waiting game, waiting to see how long and how many soldiers it takes to wipe out all the aliens.

Answer 22

The Greeks Cannot Defeat the Aliens on the Battlefield

15,000 men with assault rifles and tanks can defeat any Bronze-Age army. Herodotus made the claim, which no historian takes seriously, that the united Persian Empire that Alexander conquered was able to put together an army of a million men. Even if you took that literally—and found some way to feed them, some coordinated command structure, the men didn’t all infect each other with pathogens as soon as they came together from all over—an armored division would defeat them.

Mow down the first row with automatic weapons, and the rest will break and run. Attack infantry with vehicles that can outrun them, mow them down instantly and are impervious to any damage they can do, and the infantry surrenders. And the new Macedonian rulers are not going to be able to inspire their conscripts with the kind of superhuman morale to overwhelm a modern armored divisio until it runs out of bullets (although you might make the aliens extremely loathsome, I guess). Besides, the aliens probably could get a K/D ratio better than 20-to-1.

But The Aliens Might not be Prepared

However, the aliens might not have known they’d be facing any effective opposition.

They might not have realized there was intelligent life on Earth at all. Maybe their own history misled them into thinking that an empire capable of effectively opposing them was not even possible. If you make the natural history of their planet different, this has the great advantage of making them less like humans in rubber suits. So, for example, maybe their food source led them to a different lifestyle than the agricultural revolution on Earth and they didn’t expect a species at this technological level to have any social organization larger than a tribe. Maybe their world had no life forms similar to horses or trees, so they had no idea there would already be large boats that float on water. Maybe none of their ancient civilizations had both copper and tin, and they think of bronze as something that’s discovered as part of modern chemistry. Maybe they don’t believe it’s even possible to sustain a large empire before the equivalent of the telegraph or radio, because in their history, no one ever did, and therefore an enemy capable of amassing hundreds of thousands of soldiers with bronze weapons, horses, camels, boats and so on is a shock to them, too. Maybe that was all so long ago that they’ve even forgotten their history. (Remember, there are religious fanatics on Earth today who have convinced themselves that the Stone Age never happened.)

This doesn’t mean the Macedonians could win against the forces you gave the aliens, but it might mean they didn’t bring an optimized fighting force.

The Aliens Might Have Handicapped Themselves

Let’s say you’re expecting to land on a fallow planet where you aren’t expecting to need to fight. Maybe you decide that it would be better not to bring any blueprints for advanced weapons with you. for idealistic reasons or because you’re trying to avoid the paradox of security where every new colony has to build a superweapon because, if they don’t, another colony will build its superweapon first. Then they land and realize the local apes are actually dangerous. So they’re stuck trying to reinvent weapons they can actually build right now, from first principles.

That’s a scenario where the humans at least have a chance to stomp the aliens before they can start to snowball. By accident, really, since the ancient humans would have no idea what the aliens can do or what materials they would need to do it.