What kind of technology enabled wealth gap in feudal society? It seems it was more about religion being used to subdue people.
In short: Weapons.
On the pre-gunpowder battlefield, the mounted, armored knight was roughly equivalent to the modern light tank.
It is incredibly hard to take out an armored knight with the kind of weapons or tools which would have been available to peasants or serfs, so it doesn't take that many knights to keep enough peasants in-line to build a very wealthy kingdom.
Religion during this era functioned much more like the modern civil service than what you or I would recognize as a church, and this also included both education and state security functions.
When firearms became commonplace, this game totally changed. Previously, weapons, even the longbow, took years to master well enough to be combat effective. With muskets, you can turn a group of ignorant peasants into a fighting force capable of taking on armored cavalry in a few months, possibly even weeks.
The Enlightenment, as well as our ideas about "equal treatment under the law", were the direct result of this force parity.
Industry to make gunpowder cheaply and reliably rather than as one-offs for anti-castle siege weapons, and metallurgy and tooling to make the weapons hand-held and not prone to exploding in the operator’s hand, are what I have to assume old Asia lacked.
I'd argue the advent of centralized currencies did more harm than any and all standing armies combined.
When you think about what a parasitical entity does in biology, you realize that simply killing a host is not evolutionary advantageous--their are 3 types of parasitism, not to be confused with the 3 types of symbiosis of which parasitism lies in.
So instead the parasite seeks to keep the host alive as long as possible in order to extract resources/life from it in order to propagate and spread itself and its DNA/RNA into Nature in order to infect other hosts and rinse and repeat.
Simply by demanding that peasants/serfs pay taxes and conduct all commerce in the coin that bares the issuers legacy has brought about so much of Human misery and perpetual serfdom that it baffles me what immense gravity their is in just the last 10,000 years since the supposed advent of Agriculture and therefore modern Society.
I've spent the last ~15 years of my life focused on this very topic, and while I have gained a great deal of insight and probably did a PhD's worth of research, it would take my entire Lifetime to really dissect all of this.
People have been warring and exploiting others since civilization... I can't say 10k years back before the move towards grouping in clans and cities...
But technological currency also could "right the wrongs"...
Imagine if each person could only have 1 bank account on a blockchain, verified by identity which is somewhat centralized but governed by a DAO.
This bank account is auto-taxed (tx fees), it has a max limit, say 999 million. So essentially, there could not be billionaires. Sitting coin is taxed as well after awhile, and estate transfers would be limited say max 50 million can be transferred to posterity. The rest is paid out to all users as a dividend.
The bank account would also pay out UBI to people based on the size of their wallet and their utilization. The more purchases, the more utilization the more your payouts from UBI. A large portion would also go towards a central "trust" for crowdfunding of businesses, mutual aid for emergencies, and for healthcare.
The DAO would invest in worker/consumer owned grocery stores and try to peg the value of the dollar to prices by owning some of the pricing. Basically start w/ competing with Amazon on some consumer goods via the internet, and brick/mortar stores.
DAO would work w/ devs to develop an algorithm that ensures not too much deflation/inflation, max limits, good taxation, good ubi, good burning/minting via staking protocol, etc... all while being open and transparent.
Are you seriously pitching me the DAO, like I don't know it was one of the biggest exit scams in all of Cryptocurrency History?
Listen, you ETH guys worship Vitalik and walk around pounding that koolaid that you give us all that work in the space a bad name, give it a rest... I mean it, money is something ETH just isn't good at. In fact, I still cannot see any value or a usecase in ETH to this day besides a bunch of pump and dump schemes that tarnish what BTC and other alts have done.
I was forced to use solidity and hyperledger at an enterprise level for a megacorp, tied what the ripple and stellar idiots that were brought on without my consent to a project I had been brought no I had no choice but to leave the project and the Industry for some time. We had to loss weeks/months of work to make something that had worked in BTC (multi-sig escrow) for years just because it sounded better if it had a functionality in those 3 useless alts.
To this day I still cannot believe Vitalik, a former Unsystem developer, didn't just make this all up and his hiding all of exit scam money to contribute to the BTC network in some way; none of it adds up at all, how do you from squatting and working on FOSS in Spain to being best buddies with Putin? Chances are had he just held onto a fraction of his BTC from back then they'd all be millionaires since 2017.
But to answer you question:
Centralized currency: The means to issue and control the medium of exchange in any system (eg: civilization, country) and impose arbitrary and even malicious actions to detriment of those who reject or oppose your currency. Often a role held by Nation States and by extension Central Banks that preclude said entities.
Just tell the peasants you're the hand of the god, and the god wants you to give their cows and grain to you. I think that worked pretty well for a looong time.
It did, until it didn't and you can read all about peasant revolts in a book all you want, which led to things like the Magna Carta.
But I lived in Italy and worked on a farm that sprawled for many KMs in what was a feudal lord's manor and it was baffling just how much absurd complexity from a supply chain and logistics view tending that much land entailed since it was so fractured and disrupted by hills and valleys, and the amount of bureaucratic BS that had to be created and subsequently put up with in order to survive as a serf: it wasn't just cows, wine or grain that had to be rendered, but actual members of your family were taken into the homes as slaves, physical or sexual.
I did the mistake of watching Passolini's Salo when I was there, and the level of somberness still stays with me to this day [0] when I think what horrid forms of cruelty Humans are capable of when they amass so much power and wealth. And this was just a modern take on things, just pondering the things they did openly during the dark ages and even in the height of Rome can send me to some dark places.