Dark Ages were not so dark

The middle ages, often called the dark ages, started with the fall of Rome and ended with the voyages of Columbus. During this time great technological progress was made. Important inventions include the magnetic compass, stirrups, gunpowder and the firearms to use it, horse collars, the stern rudder, printing, the wheelbarrow, the trebuchet (a weight powered war machine), the art of distilling and hard liquor, three field crop rotation, mechanical clocks, eyeglasses, a whole new architectural style (gothic cathedrals), water mills, wind mills, crossbows and the making of cast iron. Plus others that escape my memory.
The last notable invention of the preceding classic era was the discovery of iron working by the Hittites, around 1500 BC. For the next 2000 years, no improvement in the arts and sciences came forth. The last Roman emperor (478 AD) used the same weapons, ships, agriculture, metallurgy, chemistry, and building techniques as were available to the Hittites two thousand years before.
Any general theory of history needs to explain the technical stasis of the classical era and the great progress made in the "dark ages".