I realise that after the Horus heresy, worlds were separated and could no longer communicate with each other.
But why did advanced technology disappear?
I realise that after the Horus heresy, worlds were separated and could no longer communicate with each other.
But why did advanced technology disappear?
The Imperium didn't lose all of its advanced technology but millions of worlds who were now disconnected from the Imperium after the Warp Storms started lost their technological edge by being unable to renew their resources from other Imperium worlds. Overdependence on one technology was one of the reasons the Imperium fell into ruin. The other was a series of misfortunes which crippled the Imperium.
The Dark Age of Technology, formally referred to by Imperial scholars simply as the Age of Technology, was the zenith of Mankind's scientific knowledge and technological power in the Milky Way Galaxy, which lasted from the 15th Millennium until the onset of the Age of Strife in the 25th Millennium. It saw the development of the first true human interstellar civilisation and the birth of a united human stellar confederation centred on the human homeworld of Terra. Even tens of millennia later, Mankind has not been able to equal or regain its former height of achievement attained in this era.
Humanity was very dependent on technology. It allowed them to conquer and control huge portions of the galaxy and was even before the major advent of psychic ability, one of the primary reasons for human success in the galaxy.
One of the reasons humanity was so successful at conquering a large part of the galaxy was the development of the artificially intelligent humanoid constructs now only known as the Men of Iron. These powerful and fully autonomous labour and combat robots won many wars for humanity, but for some reason turned against their masters at the end of the Dark Age of Technology. The war was eventually won by humanity, but at a great cost. The damage was catastrophic and had shattered much of humanity's power. Unfortunately, this was only the beginning of mankind's misfortunes.
This period of achievement was so great that when the Age of Strife began, Humanity did a complete 180 and decided that since technology had not saved Humanity, there must be something inherently wrong with it and began to distrust and fear technological capabilities. When this occurred there was a destruction of resources and loss of technological ability.
This Golden Age for humanity would not last. Warp travel became increasingly difficult and ultimately impossible due to the great Immaterium Warp Storms that would herald the violent birth of the Chaos God Slaanesh and the Fall of the Eldar that began in the 25th Millennium. The economy of the human federation had already been damaged by the terrible wars against the Men of Iron, and the growing frequency and extent of the Warp Storms caused trade and communication between the human colonies to collapse, restoring the isolation of human-settled planets and star systems. Within this relative isolation Abhumans, new human mutant subspecies like the Ogryns, Ratlings, and Squats, adapted to their environments and developed on several planets in the galaxy.
After the great warp storms started, worlds that were far away from the Imperium could no longer be reached and five thousand years without support, technicians, resources, training, education and military assistance meant many worlds fell into disrepair.
The Imperium has an incredible human population, and millions of worlds, but it only functions because resources move from world to world at an incredible rate. Galactic commerce is necessary because not every world has the capacity to grow or create everything it needs. Many worlds are dependent on entire factory planets or forge worlds, to get the raw materials they need to maintain their existence at their current level.
When communication was lost with the core of the empire, many worlds reverted to barbarism, violence and destructive ways. Technology and the ability to create, maintain and invent new technology fell behind on most of these worlds, especially if there were already challenges in maintain population control, food resources or other social amenities. Planets out of balance fell further out of balance. Even in the core of the Imperium, some knowledge was lost due to constant warfare, alien interactions and civil disputes.
Firstly, the Imperium did not exist before or during the Age of Strife. It was actually a human confederation of star systems. Like Star Trek but without rubber forehead aliens. The Warp storms and alien invasions, most of those aliens having been allies whom humanity protected from space monsters (hence the Imperium's hatred of xenos, because of their betrayal which rivaled the Horus Heresy in both damage and treachery). This also contributed to the lose of technology, much like how North Vietnam killed anyone in South Vietnam who wore glasses because they thought it showed an educated person. The aliens did the same thing, so to speak, by killing all well-educated humans on the worlds the conquered.
On the bright side, during the Iron War (war with the Men of Iron), almost no one was stupid enough to attack humanity. After all, the killer robots that make Necrons look cute were being defeated by a civilization that had all but forgotten how to train soldiers, despite massively outnumbering the mostly unarmed humans and being nearly indestructible. Yeah, any alien faction dumb enough to dive into that was ground up and spit out by both sides of the war. That was a lucky break for humanity in a weird way. Also, a Gaunt's Ghost novel has Men of Iron that are corrupted by Chaos coming out of an STC. This could easily explain why the MoI went rebel in the first place. After all, psykers were used by humanity to finally defeat the MoI and those psykers, almost immediately after humanity's victory over the IoM, exploded into warp portals for the literal Legions of Hell to stream out of. That practically gritos Just As Planned.
The Imperium, however, lost a lot of it's technology very slowly over the course of ten thousand years. The reason for this is pretty much just forced plot by Games Workshop to make things more grimdark. After all, fluff specifically details how Forge Worlds were created. They were rarely "discovered", they were founded as colonies from Mars. These martian colonies were fully equipped with all the technological, scientific, ect. knowledge and machinery of all the Martian Brotherhood. Needless to say, this means there is no real exscuse for the lose of technology, since EVERY Forge World founded during the Great Crusade would have the full level of Imperial technology from that time.
In addition, fluff also explains that, when new patterns and/or STC data is created/discovered (respectively), it is uploaded to a network that shares the data with all Forge Worlds, with a massive depository on Mars which holds all Imperial technological and scientific data thus far rediscovered. Needless to say, GW needs to read it's own lore before making a new codex. But, of course, an Imperium with Webway mastery, reliable plasma weapons that can glass mountains (Horus Heresy novel had that happen, Magnus was fine, though), and generally being even more ridiculously powerful than the canon Imperium of Man would make them a Boring Invincible Hero.
To top it all off, the Mechanicus somehow forgot how to maintain the Golden Throne. This is in-spite of the fact that they have performed routine maintenance on it every single day for the past ten thousand years. This is ignoring the sheer impossibility of esquecer how to maintain the most important piece of technology to ever exist. Pretty sure the Techpriests would have been extremely (fanatically) careful to protect and preserve that knowledge.
TL, DR
The Imperium's technology has gone down hill over a period of ten thousand years of extremely slow-but-steady degeneration of science turning into mysticism. As ritual replaces mechanics, important parts of maintenance and construction are thrown away for not being mystical enough, or do to lack of understanding how important those minor adjustments are. Technpriests then start substituting oils and methods they deem particularly "holy" over the prescribed procedures for the machines they maintain and produce, damaging them and weakening the product. This has gotten steadily worse over ten millennia until it is now official policy and part of a state religion to screw up technology. This, combined with Games Workshop wanting to have a plot people will actually play without Curbstomp Battles has lead to the Imperium of Man's current technological state.
It is worth noting that some fluff contradicts itself. Such as how Forge Worlds are founded with all the knowledge and industry of Mars, yet later fluff says that specific worlds are the sole manufacturers of particular technologies. This fluff apparently ignores the fact that other fluff on previous pages of the same Codex/Supplement/Expansion specifically states that the technologies distant Forge Worlds hold a monopoly on were instrumental in the Unification Wars on Terra. Long before the Imperium ever reached Mars in the first place.
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