Gfrktyl

You've pretty much answered your own question insofar as if there is no need for technological advancement, there won't be any.

If your farms are producing all the food you need and the climate is consistent and temperate all year around, there are no barren areas, no strategic points of coastlines or ports that are envied by the rulers of opposing nations, no resource shortfalls...

...you get the picture...

Then there's no need to develop anything like better weapons, ploughs, or technology in general. Putting this another way, there is no reason to advance if your life is fine as it is.

This in point of fact leads to an interesting anthropological theory I once heard that said that technological advancement only happens in cold climates. The reason was that the cold made life uncomfortable, and provided a forced scarcity of food over a winter period. This meant that people strived to find ways to make their lives more comfortable and as such, developed and refined new ways of doing things and new tools to do them with.

Regardless of that theory, if you look at the relative technological level of European explorers and African tribes in the 18^th and 19^th centuries, it is clear that Europeans with their harsh winters and relatively scarce resources had advanced more than the African tribes with their temperate climates and a bountiful and relatively constant food supply.

So; make your civilisation relatively happy and content, and advancement won't be as fast as if they're struggling and uncomfortable.

All ancient civilisations were essentially shaped by theology, so you simply need to make yours prohibit - and severely punish - technological advancement. I suggest you refer to the Safehold series by David Weber for an excellent example of how this could be achieved.

I have a few thoughts on this based on groups on some historical context (and their modern philosophical descendants):

1. Groups which shun technology for religious reasons


2. Groups which cut themselves off from the outside world due to fear


3. Groups which fear technology itself and were it will take us in the future

Amish - religious angle

The Amish have definitely hit a stopping point when it comes to technological advancement (they are not adversarial toward it but severely limit its use). They've chosen to live simply in order to better serve their religion and idea of what it's god would wish. Indeed, this does not only limit technology use but limits the needed education (most stop school at 8th grade) that would be required to engineer new devices/tools.

Isolation or Fear of outside influence & loss of control

Though certain specific technologies grow better with war, new general technological advancement requires periods of peace (see statements by Sir Henry Tizard and Sir Stanier, pgs.7-10, Peter G. Klein's statements, and linked articles/talks).

However, when pursuit of that peace causes such a fear of returning to war that governments start to impose heavy restrictions on its populace and actively force out any outside influence (pg.13) to ensure the power base of their own government - it tends to squash any ideas or technological development due to fear it will lead to revolutionary ideas or someone gaining a powerful "weapon"¹ the government does not control. It is basically trading growth for stability - at least until someone starts shooting cannons off your shore.

Fear of technology

There have always been those who prefer to live "off the grid" and those who fear what new technology will bring. One can look at Henry David Thoreau's Walden and the transcendentalist movement of the late 1880s and see elements of these ideas. While the Luddites of that same era - actually smashed new technology out of fear it would eliminate their livelihoods.

In modern times, we see the Neo-Luddist who range from the off-the-grid survivalist to calls for moderation - all the way to people still committing violence for fear of what technology will bring.

Or why not all three

It would not be hard to imagine a group which saw these driver-less cars coming (lets say Uber and Taxi drivers) starting a movement against this specific technology, began excluding countries and peoples who supported them. Then being expanded their philosophy to slowly include all technology as evil ("un-natural") and eventually take on religious undertones as justification for their fears.

^{1: Weapon here could be an actual weapon but also any form of new technology which allows you to generate income, food, or even good will at a rate that allows you to be a threat to those in power (whether you intend to us it or not)}

Pretty simple solution. Deny access to higher education. Or make it only for an elite group, several countries doing this right now. People can only work with what they actually know or have access to learning.

No written language.

Most of the technology of 600 BCE could be passed orally from one generation to the next with little room for advancement over time, because even if you did invent a one-off advancement, it would take a lot of work to explain to every other person you want to teach it too; so, it often just dies with you or it takes many many generations to become commonplace. Moreover, if you invent a single piece of a bigger more important puzzle, you don't know what else is out there to build on to complete the bigger puzzle in your own lifespan; so, it disappears with you because no one knew how important it would one day be.

Much like cavemen existed for 100s of millenia with just basic tools and weapons, if cavemen discovered smelting and farming before writing, then the bronze age would have been just as static.

In this case, you don't need to add artificial ceilings through culture or nature, you just hit a ceiling that you can't break without first inviting this one specific thing that no one has thought of yet.

None of what they have is their own technology. They barely understand what they have.

https://www.youtube.com/watch?v=KUdhBTYPhDg

"We look for things that make us go."

https://en.wikipedia.org/wiki/Samaritan_Snare

One of my favorite Trek TNG episodes. The Enterprise encounters a broken ship. Geordi goes over to help and the problems he fixes are very simple. It turns out that the aliens are very, very slow-witted. They understand none of their tech because it is not really theirs. They acquired it from a different race.

So too your people. They inherited their tech and they greatly appreciate it but do not understand it and maintain it only through careful rituals. Possibly they were refugees and found the tech on the planet they came to. Possibly their ancestors were more intelligent and creative than they are, but like the Eloi in HG Wells The Time Machine, the descendants can use and to some extent maintain the tech but cannot invent anything new.

Progress happens wherever there's room and necessity for experimentation - e.g. where you won't starve to death if your experimental agricultural technique doesn't work as advertised, but as the competition is high, you get a lot of incentive for trying something new.

You can place your civilization in a particularly harsh environment like the Extreme North. Make them originate as settlers from an early Iron Age civilization. Place them far from the sea so that trade isn't an option, and plunderable neighbors are hard to reach. Make the setup very stable (so that disasters don't happen on a regular basis) and isolated - say, these settlers had to cross a stretch of desert or tundra that became impassable centuries later due to climate change.

Now, your civilization struggles to maintain its current technology but still has to preserve it. Innovation is perceived as unnecessary and outright dangerous. Any change in the ways of life can either starve a commune to death or threaten the authority of the local government. This is a perfect deadlock that has been observed many times here on Earth.

Alternatively, since this world isn't Earth, you can make your civilization consist of regressed colonists - i.e. the remnants of a colony that went through a catastrophe (ranging from a long volcanic winter to a plague to a simple crop failure) and lost most of its technology over several generations. Then the technological stagnation might be explained by the fact that they simply have to recover their numbers. If they manage not to forget writing and agriculture, and avoid genetic bottleneck effects, you could expect them to rise again within several centuries - but until that time they would appear to be stagnant.

Limiting Information
During the dark ages, most books were not accessible to the public. Education was limited, common folks are mostly if not illiterate. Even new discoveries at that time was labelled as witchcraft, causing people to fear discovering new technology. This was because the church had power over the people.

If you limit the distribution of information it will be easier to control the mass and limiting their potentials to grow.

Dr. Slump has a perfect example of this: Gatchan, a self-replicating Angel that eats metal.

Gatchan is an Angel born from an egg placed on Earth by the Kami of the galaxy during the prehistoric ages, to prevent further development of the human civilization seeing that other civilizations eventually destroyed themselves and the planets they lived on. Gatchan's ability to replicate itself as well as its fondness of eating metal should have ensured that humanity would remain primitive and innocent.

However, in this particular story, the protagonists happen to come across the egg during a time travel trip to prehistoric times, and end up taking it back to the present, thus subverting Gatchan's original purpose. (Some causal time loop hijinks here.) Kami is considerably confused when he arrives later on to check on Earth and discovers that it had become technologically advanced after all.

Lack of Competition.

One of the biggest incentives to come up with new technologies and new ideas is if you are competing with your neighbors for resources. Europe, with more than a dozen different power bases in a relatively confined area, was constantly dealing with rival nations looking for some kind of an edge. Once you come up with something that gives you an advantage, your neighbors will be forced to do the same to stay competitive. With only so many resources to go around, the most innovative nation is more likely to end up on top.

Compare this to China's situation. Even though they invented gunpowder, moveable-type printing, the compass, as well as many other innovations, all which were instrumental in aiding other nations to make huge technological leaps, they were never used to their potential in Asia until much later. Ancient China had a vested interest in suppressing innovation, as new ideas might give other nations or internal factions enough leverage to threaten the status quo. Hence the reason why in China gunpowder was traditionally used for fireworks, little more than a curiosity, as opposed to cannons and muskets.

This eventually came to haunt them when England and other nations came calling, as their lack of innovation in technology left them vulnerable to more advanced invaders. Japan also experienced this phenomena, for similar reasons.

So if you have one single nation, and no competitors, you have a good reason to avoid technological change.