If medieval advances in the plough didn’t lift Europe’s peasants out of poverty,
it was largely because their rulers
took the wealth generated by the new gains in output
and used it to build cathedrals instead.

And this has happened many more times across the world/along human history.

The fact that Stonehenge exists is ample proof that those people had been able to generate enough ‘wealth’ to build it.
We’ve been able to find out that the boulders had been sourced from two places. The 20 tons hard-sandstone sarsenes ‘traveled’ about 20 miles while the 2 tons blue-stones had been schlepped for about 220 miles. According to Mark Pitts, writing for the British Museum. And we think we have a fair idea about how the whole thing had been put together. Read the paper.
But we know close to nothing about the people who did it.

The stone ring is all that’s left of them.
Isn’t it strange? For such a technologically sophisticated people – and rich enough to afford such a herculean endeavor – to disappear in the mist of history?

And here’s a selection of other abrupt endings/’hibernations’:

Mohenjo-Daro and Harrapa in Pakistan.
Angkor Wat.
The Great Chinese Wall
The Egyptian pyramids
The Athenian Parthenon
The Roman Coliseum and the roads cris-crossing more than half of Europe
Kuldhara, the ghost-city
Machu Picchu
And, last but not least, the cathedrals mentioned by Reuter’s Mark John.
Europe did take a break after finishing building those cathedrals….

What am I trying to ‘suggest’?

That we, as a cultured species, have a tendency to evolve in fits and starts.
We tend to reach pinnacles only to descend – sometimes temporarily – in abject ‘marasmus’.

Could ‘self-sufficiency’ explain at least some of this?

While the spinning jenny was key to 18th century automation of the textiles industry,
they found it led to longer working hours in harsher conditions.
Mechanical cotton gins facilitated the 19th century expansion of slavery in the American South.

NOTA BENE!

Don’t tell me capitalism is at fault for any of this.
Capitalism is but a way of doing things. A road. Which we followed to where we are now.
How we behaved en-route and what we decide right now was/is our own contribution!