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Brainstorming a sci-fi setting, and justifying interstellar war

I recently got bit by the nostalgia bug for Battletech.

Big robots, no magic or psychic mumbo jumbo. Fun times.

But thinking back on the novels I read in the 90s and the video games over the past couple decades, and comparing them to the understanding I have today about how war works, and my knowledge of space, and my enjoyment of series like The Expanse that care about realism a bit more, I find the lore of Battletech lacking, and the logic of its warfare a bit silly.

I have an urge to run a mecha campaign for my friends, maybe not in the real Battletech universe but in my own knock-off version, so I'm trying to come up with more compelling rational reasons for conflict. Let me explain.


OG Battletech works on sort of feudal logic. Your mechwarriors are your knights. Their mechs are their armor and steed. They might be accompanied by infantry and tanks and such, but mechs serve as the focus of military engagements, which serve to help various lords maintain control of planets spread across the galaxy, and then those planets pay taxes or whatever.

But technology and distance makes running an interstellar feudal state very different from doing it in medieval Europe. The biggest factor is how faster than light travel works.

In Battletech, you need to maneuver a jumpship (which always stays in space, and are a few hundred meters long but are almost entirely the 'jump drive' with limited internal cargo) to somewhere with 'simple' gravitational tidal forces -- usually above the poles of the local star. Then you need a gigantic amount of energy to create a field that does some funky math akin to finding the square root of a negative number, with the result that basically removes everything within the field from space and then shunts it in a particular direction. You don't actually move, just calculate where - if you were to draw a straight line through the cosmos - you would next encounter a gravity well. Then the math works in reverse order, and the ship suddenly appears in a new location, which has to have very similar gravitational parameters to where it left. (So jumping close to planets is likely to get you killed.)

Once you arrive, the jumpship usually stays in place, and they launch dropships (which go between space and ground). The largest of these have cargo capacity far less than a modern cargo container ship, and a single jumpship might have docking points to carry 9 dropships with it whenever it jumps between systems.

It takes a week or two to recharge the jump drive, and getting a dropship from the arrival point to a planet takes at least a few days. (I think the setting is unreasonable in letting ships zip around at 1G for days at a time without worrying about fuel, but let's ignore that.)

Each jump takes you about 30 light years. And the setting describes interstellar nations spanning like 200 light years, so we're talking 3 jumps for stuff to get from the edge to the middle. Several weeks of travel, all to bring a relatively small amount of cargo. What resources are you extracting from another star system that warrant all the time and cost, instead of just going to asteroids and planets in the same system you live to get that stuff? How long would it take to strip mine the whole solar system for resources before it becomes cost effective to ask for 'taxes' from other systems.

Like, what are people even fighting over?


Maybe instead of conflicts being fought over resources, instead the concern is positioning. If different nations distrust each other and fear annihilation, they'd want to set up their capital planet somewhere far from enemies, so if anyone wants to invade, they'd have several lines of defense by positioning orbital bases around the arrival points, letting them blow up invaders before they can recharge and jump again.

That might be neat sci-fi, but it doesn't give you a reason to deploy walking humanoid tanks to control territory.

I guess if you need to resupply, it could work. But what sort of warfare are you intending at the final objective? You don't need a ton of people for an orbital bombardment with nukes or 'relativistic kill vehicles' (e.g., big rocks accelerated to a high fraction of the speed of light). But maybe if you want to seize a planet and control it, and you want to bring in, like, hundreds of thousands of soldiers, you might first need to control planets along the way so you can resupply all those people after each jump.

In a sort of grinding fight over land and resources, though, how expansive is the conflict? Like, these planets have been inhabited for centuries, and if we look at how long it took somewhere like Australia to bring in colonists and reach a population of tens of millions, are we going to assume all these worlds have huge populations? Are we sending dozens, even hundreds of mechs to try to claim a whole planet? Is that feasible?

Or would the focus be more on things like objective raids - sending in a small force to blow up infrastructure and then get out, hoping to keep border planets from having enough resources to serve as a launch point for an invasion? But in that case, well, just hit it from orbit, right? You'd only need mechs to go into underground facilities, and I would struggle to see why anyone would leave conveniently-huge tunnels in their fortified bunkers for enemy mechs to get into.

So instead there's the 'formalized duel' idea, where each world has someone assigned to defend it, and if you want to claim it you challenge them to a duel, and everyone agrees to have roughly equal forces and abide by the results for the sake of honor. That's the way things work with the setting's "Clans," which are a separate culture. I guess you could do it with the rest of the Inner Sphere, and most citizens would just shrug as long as the fights happened away from any settled areas. But it's . . . well it's kinda silly, right? Why even use mechs if it's all just an honor thing? Why not hand over ownership of a multi-trillion-dollar planetary economy after losing a game of Halo or something?

In universe there is some lore about how a few centuries ago everyone went 'total war' and launched nukes all over the place, and it was so terribly counter-productive that all the survivors agreed to chill a little and abide by the Ares Convention (similar in spirit to the Geneva Convention), laying out what's allowed in battles. One of the restrictions was "Don't blow up each other's jumpships," which, okay, fair. It's like 'don't screw with shipping' in the modern day.

But why tolerate letting mechs even land on your planet? Why not invest in orbital defenses to shoot down dropships with torpedoes and rail guns and the like?

I'm struggling to think of situations where interstellar war with mechs on the ground make sense. Maybe I could just skip the whole 'interstellar' part, and make it instead be conventional warfare between nations on the same planet. And like, interstellar combat would be less 'invasion' and more 'backup for whichever local nation we are allies with.' Y'know, more akin to the US helping the Kuwaitis in Operation Desert Storm, and less "Crossing the British Channel on D-Day."

Or or or or again, another way to think of it might be more like the island hopping in the Pacific Theater of World War 2, and to have most planets be very under-populated? Maybe few planets are pleasant enough to support large populations, so instead you have like one city of 100,000 people, and some farmland and mines around it, all designed to support a spaceport that launches resources so they can build ships in orbit and sell food to passing jumpships? If we imagine that the setting has some super-efficient fuel so getting out of a gravity well isn't that big of an expense, it would be safer to grow food on planets with atmospheres instead of doing it in domes on moons or asteroids with lower gravity.

I've rambled a lot. If you have ideas or opinions, lemme know.

I suppose ultimately what I'd want to design is a single military operation - from arriving in system, to traveling to the planet, to landing, to fighting and negotiating, to getting out or setting up long-term shop. Maybe I could just pick a real life battle and model it on that, but ideally I'd find a way to focus on a smaller number of characters, instead of having thousands of soldiers like real war does.

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First thing I would suggest is a Balkanized universe. no large interstellar nations. You can get to that in various ways from Feudalism, to Corporatism. The how is relatively unimportant, when compared to creating a situation with limited resources. This would result in smaller units being the norm.

Next, given the limitations on transportation that you've mentioned, you need something finite, rare, and portable for those groups to fight over. The two things that come immediately to mind are some mysterious "Dilithium Crystals" or the like, that are a necessity for jump engines, or some sort of other Macguffin that would attract people to a place. How about Forerunner tech? Stuff left behind by some ancient race that gives a definite advantage, if it can be reverse engineered. it could take decades for it to be figured out, so doesn't necessarily need to come into play during the run of the campaign, or it could be used to unlock certain tech like PPCs, for example, for combat use.

Just spitballing.


The Mass Effect setting resolves some of your issues. Its equivalent of jump points are Mass Relays, massive ancient devices that allow long-range cross-galactic travel along specific routes. They're nigh-indestructible, and beyond that nobody wants to mess with them because (a) none of the current civilisations have the resources or know-how to build new ones, and (b) when they do go up, they take out the whole star system with them. They're also hard to blockade, because emerging ships can materialise anywhere within a few hundred kilometers of the relay.

Beyond that, ships have FTL drives capable of traversing distances between stars in a matter of weeks (and between points in a star system within hours), so interstellar civilisations tend to form in 'bubbles' around a relay - they can expand further out to more distant star systems, but the further you are from the nearest relay, the more disconnected you are from the wider galaxy.

And finally, the entire basis of the setting's advanced technology is Element-Zero (Eezo), a rare element that affects local mass when electrically charged. It can do everything from power FTL drives to give people telekinetic powers, and it's formed only during high-energy events such as supernovas, so it's not something you can just find lying around in plentiful quantities in every settled star system - it's something you need to go out and acquire if you want to build your advanced tech, so it's an incentive to explore, trade and wage war.


If you're just looking for a reason to have cool mech fights, why not postulate a post-scarcity Universe, where everyone's got enough resources to keep them healthy and comfortable, with a decent lifespan...and they've discovered living that long can get pretty boring. So the mech fights are there primarily for entertainment: the mech "teams" show up on a new planet (so nobody gets a home field advantage), and they have it out, all of which is televised throughout the galaxy and observed by the rabid fans, who get to see new mechs getting fielded for the first time, new planetary conditions with each televised fight, and there's always the thrill of knowing some of those mech pilots might actually die (analogous to how some people watch NASCAR races hoping to see a cool crash).

Just a "top of the head" thought.


I like the Balkanized idea. Even if you do have large interstellar nations, the conflicts would happen in places that are not in alliance with them, sorta like what we have these past few decades in eastern Europe.

As for rare resources, a deep dive into the Battletech wiki reveals that someone decided that jumpship drives require a lot of Germanium, of which we've discovered only 118 tons so far on Earth.

I suppose I could just use that, but for my own sense of needing to explain the weird physics of FTl, I'd want to have some wonky variation of it, like the antimatter version which you need in equal quantities or something.

So yeah, there could be lots of worlds that are kinda inconsequential. People colonized them to look for resources, and you might have thousands of millions living there, and no one bothers to invest in major defensive weaponry because no one has a reason to attack. Most places would just do their own thing, maybe try to cater to rich off-worlders as tourism destinations in order to get, like, various biological things that are hard to grow natively.

Chocolate, or coffee, or whatever.

But if they find deposits of minerals that are valuable, suddenly different moneyed groups have a reason to want to control and protect the planet. Nuking a civilian area would elicit interstellar sanctions and consequences, so nobody does that, which creates maybe a perverse incentive for defensive forces to set up inside cities.

Maybe the planet Deyemji finds some germanium, and so now the Capellan Confederation and the Federated Suns both want to bring the planet to their side. A civilized option would be to see who can pay the most or whatever, but these big nations have hammers, and they're gonna swing 'em.

The most important installations on the planet would be the germanium mine and the spaceport - dropships can land and leave on their own, but bringing your own fuel with you is just expensive enough that it makes controlling the spaceport vital. So the Capellans land a battalion of mechs - three companies of twelve mechs each, one at the mine, one at the spaceport, and one on rotation in a major city. The Capellans want to hold the place long enough to build up the necessary infrastructure to build orbital defensive platforms and maybe a pair of fort stations above the poles of the local star.

Bombarding the planetary sites is counter-productive, but the Feds want control of the planet before the defenses go up, so they send in forces of their own, and try to seize the important sites. Once they do, they'll try to bring in more materiel - like anti-ship batteries - after which they hope the Capellans won't want to keep wasting resources on the fight. But maybe the conflict keeps escalating over time.

That could make sense, yeah? At least as justification?

Now I need to ponder how the actual combat would go.

If you have $10 to spare and don't mind reading scans of books from 1995 (with a couple of missing pages no less - cripes, what clowns) I would recommend grabbing the Mecha! + Spirit Warrior Empire bundle from Wargames Vault. The setting the original publisher (Seventh Street games, long defunct) developed for this set of mecha miniatures rules is one of the quirkiest things ever written, and even if you never use the actual minis game rules (which are fine, but not an RPG unless you count early Car Wars as an RPG) they offer a pretty good basic answer to how to suspend your disbelief and play a campaign of interstellar mecha warfare. Precious few descriptions of the game online these days, but a Q&D synopsis would be like this:

All the Aztec gods are actually a clan of nearly-godlike aliens who are fighting a war to the death with a bunch of their relatives to gain a reward from an even-more-godlike alien. They're bound by completely arbitrary rules that are meant to keep from blowing up the universe and have to use merely-mortal proxies to do the fighting, equipped with (by their standards) crude technology like mecha suits and gigantic interstellar space-fold ships as transports. The central clan of aliens originally recruited a bunch of Neanderthals from Earth as an army, but when their numbers started running low from casualties and they went back for more they discovered they were extinct (partly because they took so many in the first visit). So instead the clan pretended to be gods and recruited a bunch of handy Aztecs, transporting them to a new homeworld and training them to use "warrior skins" (mecha) to fight the proxy species of other alien clans - and each other, because the competition makes them better fighters and the individual gods kind of hate each other and all want to be in charge of the clan. Meanwhile the Aztecs are also still fighting Flower Wars with stone-age weaponry on their new planet because tradition and bloodthirsty stupid alien gods, that's why. Most of their advanced tech is produced for them by the gods and their autofactories, and might as well be magic from their POV. There's also a group of former Aztec neighbors who were recruited to hold off the Bad (well, Worse) Guy aliens while teh Aztecs were getting up to speed, and they've secretly interbred with some Neanderthals who escaped the war and hid out in asteroid lairs and actually sort of understand what's going on, and at least two different proxy-warrior species in the service of other almost-god-alien clans, one of which is supposed to be extinct...etc.

Let's face it, just using mecha is already suspending enough disbelief to crush neutronium. You might as well lean into it hard and have a gameable, tightly constrained interstellar war fought for the glory of horrible alien pseudo-gods by soldiers who mostly have no idea what's going on. At the very least it's an entertainingly gonzo read and a good source of inspiration for doing something slightly less crazy as an RPG. An inconceivably-far-future setting where they build war mecha solely because they look cool and fight their "wars" as much for entertainment as anything would be a decent approach - maybe all that counts is your side's ratings on the Pan-Galactic Streaming Network? Trading godlike aliens for godlike AI viewers is so much more realistic... :)

This reminds me of when a friend ran a D&D campaign where we all had to play lizardmen. Our city of lizardmen was going to have a big Aztec-esque sporting event against other lizardmen to see if we could go to the championships, where they'd play the forces of the dead to keep the sun from being extinguished.

We weren't playing the sport, though. Our mission was to appease the fire god of a distant volcano to ensure the jacuzzi the team used was the perfect temperature, and so we had to bring that volcano god offerings - two wagons full of humans. The damned humans kept trying to escape and would then get summarily caught by giant bats or inviso-panthers or whatever.

The we came upon a trio of mind flayers working to extract the brain of a beholder, whose mindless body they proceeded to mount on a tall tree. When they spotted us, they got antsy that we'd tell someone they were setting up a pirate node to transmit the upcoming sporting game without making the necessary offering to the god of entertainment (i.e., they were pirating), but we got them to be cool by pretending we were a traveling snack cart: we traded a few humans for some weird psychic items they had.

From there it was a pretty perfunctory ascent up a volcano to chuck a handful of mammalian humanoids into the lava. Then we backtracked, took the beholder head for ourselves, and smuggled it back into lizardman city to see if we could sell it.

Covid hit sadly before the game could go any farther.

Journey Mountain Studios

Building Galaxies
I'm going off of old memory, so apologies for any lapse in accuracy, but I remember for Battletech most of the rules and reasons for things are to make Mech vs Mech battles as cool and as likely as possible, despite all reason.

Sure the empires fought for populations (taxes, labor), positioning (invasion points, choke points), much like today. But the Battletech lore explains that what these empires are really fighting over was what remained of advanced civilization, the high tech factories. The story is essentially a post-apocalyptic interstellar mech brawl. All the things we take for granted like automation, nuclear power, computer chips, targeting and tracking systems, space mining gear, water purification, are very rare and only a handful of planets have factories that make those things. To prevent these and things like Jumpships and Mech factories from being destroyed by open warfare as had been happening for hundreds of years, everyone agreed not to target them or scorched-earth them and instead do raids or battle for the planet off to the side a bit.

Plus it was easier to just grab an already established industrial base than try to set up the mining equipment yourself. Until they finally discover ancient blueprints and equpment, Battletech is a war fought with leftover scraps (hence the handing down the mechs that still work, from parent to child). But it's a scrapwar where the remnants of ancient tech, the mechs, are an insane force multiplier against contempory companies of tanks that barely outstrip what we have today. So instead of trying to invade with an army of vehicles and troops in hundreds of dropships, you invade with a regiment of walking death machines in just a few dropships. Again, the entire lore is contrived to make mech battles worth having, especially on a tabletop map, where your company alone gets to decide control of an entire planet (or at least just the factory there).

Also, yes it took a week or two for a jumpship to recharge using it's own solar sails and batteries, but in civilized space where trade is common, jumpships recharged more quickly at stations at the jump in point. Some jumpships, especially the warship types, had double sets of batteries so they could jump in and then jump out again without recharging. And yes, planets that could afford it, or had the techincal know-how, did invest in air defenses and fighter cover to destroy incoming dropships...but not many planets could afford to have these either and the invaders just landed away from what few defense sites there were anyways.

All of this is to say what others have said above. Make up whatever reasons you need to make Mech fights worth doing, because Battletech sure did.

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