Argthtjtr

There was an ancient war between two advanced alien civilizations that culminated in a battle over Earth. These two armies destroyed themselves in this final battle, but the fallout indirectly ravaged the planet. As a result, earth has become a wasteland stuck in the dark ages, filled with genocide, slavery, starvation, and all the usual horrors of warfare on a global level. Civilization has regressed back into tribes, each struggling to survive after the apocalypse. This state has lasted for thousands of years.

This battle left space debris orbiting the planet, which occasionally falls down to earth. This debris usually contains advanced technology and weaponry, which the inhabitants constantly battle over. The result is a planet occupied by techno-barbarian tribes, each fighting the other for access to this tech and domination over their enemies.

Civilization is a hash of various, barely understood tech. Vat-grown abominations made from artificial wombs, cybernetically enhanced amazons, genetically enhanced soldiers, machine drones controlled by A.I., the list goes on. History is filled with various empires rising and falling in quick succession, followed by periods of dark ages.

In this chaos, one city state has managed to remain stable through the various millennia by hoarding as much tech as possible. They have gathered the most consistent forms of technology through organization and study. As a result, this city state has the most knowledge and understanding of the tech they use.

It wishes to remain neutral in the various wars raging around the planet, and do not take part in the chaos. They are unaligned with any faction, and do not take sides in conflict. To preserve this neutrality, they have agreed to trade technology with various tribes so that all would see a benefit to letting this stare operate. However, While they are powerful, they are tiny compared to the tribes roaming the planet, who could destroy them given enough time. It is well known how this state hoards technology, and is sitting on a vast pile of advanced tech that would make any tribe vastly powerful, perhaps enough to build a long sustaining empire.
a strong enough techno-barbarian with enough allies could potentially overthrow the state and take what they have simply with strength of numbers and more technology.

In this world where control and domination of technology is the most important thing, how can this state remain neutral and protect itself?

Early in the post-alien-war history, the founders of the neutral city-state discovered the only intact and functional shield

The shield-generator (and perpetual power source) is large and not practical to transport, so it naturally encourages "stay here and be safe" over "go out and conquer". This would also limit the size of the "safe" region, which may partly explain why your city-state has remained small.

I would propose that this alien shield can switch between absolutely barring entry to the region and temporarily neutralizing all tech along the border. The second option will often be more strategically effective - when your vat-grown abominations control units stop working, or the bionic amazons prosthetic limbs suddenly won't move, or the invading army's energy weapons are suddenly just hunks of metal and plastic, etc...

I propose some explanations for this neutrality :

• enormous military/technological advantage (which is, according to your details, likely to happen)


• spiritual/intellectual untouchability or supersition : for example barbarians believe the city is holy and gods or monsters punish everybody trying to attack it


• economical dependancy : the city is the only place where an essential specific thing is created (drug, fuel, processors, ...) and barbarians could understand that keeping the city alive benefits to all


• making alliance with litteraly all surrounding tribes (military defence, material supplying, ...)


• physical isolation : the city is really hard to reach so the barbarians think it is not worth attacking it


• the barbarians are not united or organized enough to invade the city properly

etc

Your city-state has the “Sword of Damocles”.

A extremely powerful and accurate weapon system that can take out any tribe (or at least its leadership) at any time. No matter how and where they are hiding.

(I’m thinking about an orbital launcher platform with tactical nukes that they have remote control off. Or something to the same effect. Literally having the sword hanging above their heads....)

Everybody else knows they have this tech. They have used it a couple of times in the past to take out a particularly obnoxious tribe. And they are not afraid to use it again. And that is also widely known.

Of course, they do offer neutral ground to all tribes as a major trade hub and offer repair facilities and they will sell some tech (the least dangerous to the city-state stuff) to everybody who comes with peaceful intentions. But there is always “the weapon” hovering ominously in the background to make sure the barbarians act in good faith.

Neutrality itself isn't very hard to achieve: they need to refuse any and all offers of alliance by any of the existing techno-barbarian tribes and make it widely known that they won't associate with anyone and only wish to be left alone to live their lives. And make sure to avoid any gesture that could be interpreted as an alliance at whatever level with any of the tribes.

That would require either some high-level diplomatic skills or the application of overwhelming brute force; ie vaporize any member of any tribes that get within a certain distance of the city-state, no questions asked.

Trade

The city hoards as much as it can. The tech it has already studied, and has created the means to reproduce, and aren't too devastating to be a problem to the city itself, it trades out to the barbarians, irregardless of tribe. It maintains neutrality in that it offers its services to anyone.

The city operates its own specialized army of spies that operates through subterfuge. These units scatter themselves between other tribes and steal what tech they can from them, and also scouts for potential buyers.

The tribes themselves understands the value of the city existing, in that they can get their hands on weapons that they otherwise would not, due to rivalry and hoarding. Those that do business with the tribe may offer extra to keep their own findings a secret. Tribes that attack the city find themselves being opposed by other tribes which benefit from the city, and most consider it not worth the risk.

The problem happens when one tribe gains something so valuable, the city gaining knowledge of it becomes a threat. They might try to seriously upend the city despite the risks.

The spy network keeps an eye out for such high level risks and attempts to take preventive measures, spreading propaganda to get other tribes to attack it, while also trying to steal the tech during the chaos.

1. Think Switzerland. Centrally located with difficult terrain and narrow trade roads, easy for a single wagon or light truck but difficult for armies.


2. Strong point defenses with limited throughout. The city can reliably take down some finite number of attackers, vehicles, or projectiles per minute. In theory a coordinated mass assault from multiple directions could crush them. Some famous conquerer tried in the past, but got the timing wrong and suffered huge losses. No one has tried since.