Well, that's the thing. Yes, the central control collapsed (though I still wouldn't underestimate the influence of the Church, which effectively controlled kings' actions through the threat of excommunication). However, on a local basis, there was no such great disaster, just a long slow change.

And it was not really a dark age. As I said in my previous post, the dark age narrative is largely an invention of the 17th-18th century. What actually happened in that period was the development of a whole lot of great stuff like city states, art, commerce, banking, kingdoms, navigation tools (compass), military inventions (crossbows, guns), hourglasses, farming technology (ploughing), metallurgy, optics (eyeglasses!), mechanical clocks, textile technology (spinning wheel), the printing press, windmills, glassmaking...

For the people living in those times, it probably didn't feel anything like a "dark age". Just a fairly smooth progression upwards, with the usual ups and downs of wars, plagues and other disasters that are hardly confined to the middle ages.

I know the narrative of "here's the awesome roman empire, and now the church takes over and you have the dark ages, and now reason comes back in the form of the renaissance" is very compelling, particularly if you don't like the church very much, but it is just a narrative, and is not very well supported with facts.