Humans have grown fat, complacent and cock-sure of the certainty of future progress, arrogantly expecting to [build minds in their own image](https://worldbuilding.stackexchange.com/questions/6340/the-challenge-of-controlling-a-powerful-ai). They even dream of building themselves a city, [with a tower that reaches to the heavens](https://worldbuilding.stackexchange.com/questions/8866/where-to-anchor-my-space-elevator), so that they may make a name for themselves in space, where they wish to blacken the skies with their footsteps and besmirch it with their greedy mining robots. 

Too bad for them and their silly dreams. They won't get the chance to return to the Moon, not for centuries. Why? **Because a new dark age is coming.** 

**What are the omens, the dark messages that foretell the coming of this black age?
What is to bring this dark age about?**

If that was too poetic, imagine a 90% drop in GDP/cap, a 60-70% drop in life expectancy, general loss of culture and knowledge, as well as a drastic drop in public and private safety and security. What matrix of factors could lead to such an outcome?

In order to objectively judge a "good" dark age entry point the following criteria have to be met:

1. No Daemon-ex-machina to save us from the relentless march of Progress. So out go aliens, asteroids and supernovas. **The cause must start here on Earth and be the logical** (dialectical, to borrow Marxist terms) **conclusion of our own progress** (or was it hubris?). While those are possible (and thank you for the pre-edit answers) they are now outside of the current scope.
2. **A clear and plausible mechanism to get us there from here.** If a doom-bringer is visible from a mile away, presumably people would not go there unless severely pressed from all other directions. (i.e. the Singaporeans knew the dangers of [unshackled AI](https://worldbuilding.stackexchange.com/questions/8915/shackling-strong-ai-second-attempt), but the desperate circumstances of a 3-front war while outnumbered 1000:1 forced their hand)
3. The disruption must be **unstoppable** once started, **persistent** (what's left of humanity can't simply go back to normal in 3 years) and **widespread** (i.e. Switzerland can't simply sit this one out). Pockets of relative high-tech might persist, such as the Massachusetts Institute of Theology's department of Applied Philosophy, but progress in any scientific field must be severely curtailed and even reversed.