So.... I've got a setting I wish to write up. Its an alternate timeline, where, 20 minutes into the future, ww3 occurred. There was, well, A. The guys who wanted who take over the world and institute genetic modification. The majority of the world said no Alpha faction got pissed, went to 3rd world countries, and using a combination of selling genetics services, bribery, blackmail, and even assasination, took over the majority of the world. But not enough of the world. And the remnants formed a grand alliance to shatter this interloper. And in the war that followed, a type of superhuman was created, smashing apart the armies of the Alliance, and basically took over the place. The starting generation died out... but in their place was the superhumans, along with a heap of genetic knowledge. 90 years passed. The human population is now 1 billion, dropping from 8. They are treated as chattel, as 2nd class citizens, as sentient furniture. Work camps have been set up, where dissidents, the unlucky, or anybody else are set there to be worked to death in the poisoned soil, reclaiming the earth. There are roughly 10,00 superhumans (don't think blasty, think on the level of captain america), and a lower class of 100,000 servile humans that are less superhuman, but obedient to the upper class, unable to disobey. They rule through the combination of brutality, the lack of anyone else coming to help the resistance, their sole ownership of things like heavy weapons and armed vehicles, quislings, their control of the power points of society, and their own superhuman strength. They take over the upper echelons of society, so anything of power is basically controlled by a superhuman. Majority of the cities are dead, with only 20 or so cities left. So here's the thing. What, exactly, do they have access to? Superhuman society is composed out of 110,000 beings at most, irregardless of their individual strength. The rest is working for them either as quislings, unwillingly, or just plain ignorant. There is no other significant nation-state facing them down. Do they have access to nukes, what with the sheer resources needed to build them. Do they have access to ships, with the manpower needed to build, maintain, and crew them? Can they even have access to a large standing army, what with the immensely decreased population. Even Rome only had 1% of its population in the army. Yes, they have gunships and artillery to kill off rebels and such. But anything else? Unlikely. So its basically a small majority of superhumans, with 100,000 genetically engineered slaves, with the majority of the remaining billion humans hating them. Majority of the cities are annihilated, along with arable land and industry. What, exactly, do their arsenals look like?
This: https://tvtropes.org/pmwiki/pmwiki.php/Main/TwentyMinutesIntoTheFuture They have drones, power armour, and other stuff, but nothing completely earth-shattering. Much like us. But a bit different.
Military power armor is a bad idea, unless you're designing them for EOD, MP, logistics, or CBRN. A slightly increased level of protection is not worth the loss of mobility and concealment, dependence on fuel, and weakness to narrow doorframes and bollards. They'd also be a pain to wear. There would be no breathability, causing heat strokes and rot (unless you want to carry an entire laundromat's worth of clothing per person to change out every night). There's nothing stopping us from creating larger bullets to defeat power armor, except for our current lack of need to do so, especially if we're going to be fielding our own exoskeletons to support a more cumbersome weapon.
How about automated war-machines, ships, planes, etc.. it will greatly reduce your need of man-power. Also, you can create another class of several millions(or less) who are loyal to the upper classes(thus are given jobs like flying planes, supervising the lower caste, fighting and squashing rebellions). As a result they are treated much better. Moreover such a faction could be a great tool in bringing the upper classes down(a handful could cooperate with the lower class), having intel and freedom of movement they are much better suited for a rebellion.
The potential power of a standing arsenal itself could be a central point of contention in the story. The superhumans could have the skeletons of that war up on display, making the gaping hole of a 20mm chaingun barrel a direct answer to any notion of rebellion. However, in reality, the tech decay could be greatly outpacing labour, leaving 5% of it still workable. Then you potentially have this scene from Snowpiercer: Spoiler for an actual spoiler this time: Spoiler
If there are only 10 000 superhumans and 100 000 slaves... well, you need to figure out what kind of industry they will have. See below for my thoughts on that. Nuclear war will have destroyed any electronics (EMP), and issue is - as I pointed out - in what kind of industry - and society in general - will they be able to rebuild. Now, if there are 1 billion humans as slaves... that means that high-tech society is still possible. I was uncertain whether chattel slaves would be adept enough to build high-tech hardware required but, well, China. So to answer OP's question: their military would be highly tech-intensive, and also optimized to holding the "cattle" in line. Meaning you'd be looking at basically heavy-duty police force, and, as pointed out, heavy automation.
Full automation would just open your military up to cyber attacks for little benefit. OP's given scenario is asymmetric warfare where you're trying to suppress a population that sustains your infrastructure. You can't kill them all, so you need to convince them to not fight. Vehicles can't work with locals to find town's bomb-making insurgents, so you'll need personnel. Vehicles can't repair or fuel themselves, so you'll need personnel. Vehicles can't clear rooms, so you'll need personnel.
It wouldn't be the EMP that does irreparable damage to infrastructure, but the chaos that ensues from a sudden loss of electricity. Most people don't know how to survive without clean water and grocery store food. The affected area will turn into a battle royale of looter gangs, destroying most of the remaining industry.
Not exactly... 1 billion as slaves. Some would live out in the midst of a blasted wasteland, rather their children die of chemical poisons at 10 years old than let them live under the bootheel of superhumans. Others live on ghettos. Not much hope. Not much food. Basically a shit life in the slums or projects. Others serve as the workers for companies. Doing the ground work that is so very often vital. Some take part of law enforcement. Basically cracking down on rioters, protestor, and the not. Basically the first line of defense the resistance faces. Others? They're quislings. In all senses of the word.
Yup. Thank goodness I'm going to break it. But seriously though, I think there won't be any great army. Anything that requires large amounts of manpower are right out and anything that is immune to protestor or people armed with home made bombs will probably be the greatest level of advancement. Less battleships and supersonic Stealth fighters. More APCs and maxim guns. At least, that's what I think.
Depends on the type of cataclysm that leads to this post-apocalyptic scenario. If it were plague, then there would potentially be plenty of equipment left over for an ambitious group to claim, learn to utilize, and put to use on the battle field. If it were a full-on nuclear war, not much. If it were a limited nuclear war with only a few detonations in some key locations, then perhaps something like the 1800s with cell phones and pre-war relics that curious and mechanically inclined people would be tinkering with. A billion humans left compared to 110,000 superhumans would still put a lot of potential power in the hands of regular humans. And those among the humans with higher than average intelligence would more than likely scheme and plot against their masters. It's just part of human nature. The ones who are just intelligent enough to understand their plight, but not intelligent enough to have the ambition to lead a vast rebellion would still find opportunities to commit petty acts of sabotage. That's also part of human nature. Even if only a fraction of them had the will to carry out these petty acts, a million petty acts is still a million petty acts. That's a lot of sabotage, and could go a long way towards crippling an occupying force like the superhumans. Think in terms of those middle-eastern war images posted above. The US would be equivalent to those super humans with their super advanced tech compared to the locals. However, endless acts of petty sabotage (think IEDs) over an extended period is enough to grind the US war machine to a near stand-still and cripple the US economy in some important ways. These kinds of details added into your story would go a long way towards adding depth to the idea (which I already like, and bears some resemblance to my own novels that I'm currently working on).
An immense war, involving nuclear, biological, and chemical wmds. Some areas were hit by nuclear blasts, multiple times. Entire countries were wiped out. And by wiped out, I mean 'went the way of the dodo'. Think about the devastation required to turn a population of 8 billion to 1 billion, and you'll kinda get it. Yes. I'm thinking that many of the people are in the own quisling government, working with the invictus only to feed their families or keep them safe (There are always the bastards who are always in it for the power. They have to be purged). It's just that, well, no support, no heavy weapons, no supplies, no organisation, and nothing to stop the superhumans from simply deciding 'Fuck it, time to kill them all' no one really does anything of note. Until the protagonist arrives.
That kind of story could go in two directions. I Have No Mouth and I Must Scream comes to mind as a potential outcome. A series of short stories chronicling the brutal end of individual regular humans run afoul of the superhuman race being snuffed out for the pleasure of superhumans, or a catalyst figure emerging from obscurity to galvanize what should be an already simmering rebellion.
I'm being nitpicky, but the analogy is kinda off here. For one thing, the US is constrained by many things. Rules of war. The press. International pressure and foreign agents. Their own people. The unwillingness of their soldiers to carry out atrocities. Foreign programs to arm the rebels. Here? It's been 90 years since the superhumans' victory. Frankly speaking, if they went to a city, rounded them all up, and the put them into gas chambers, they would do so without the blink of an eye. Or, say, simply deciding to gas them all with sarin.