Dark Age

The Dark Age of metal working was caused by the depopulation.

It will be many years before they again learn to work bronze.

The troubles of half a dozen Bronze Age societies, 

can be blamed on a single event,

a natural disaster.

Dark age transition

historians believe was violent, sudden, and culturally disruptive,

and involved societal collapse

almost every significant city in the eastern Mediterranean world was destroyed,

many of them never to be occupied again

interrupted trade routes and severely reduced literacy in much of this area

climatic changes

The archaeological evidence shows a widespread collapse of Bronze Age civilization

in the Eastern Mediterranean world at the outset of the period,

as the great palaces and cities of the Mycenaeans were destroyed or abandoned.

At about the same time,

the Hittite civilization suffered serious disruption

and cities from Troy to Gaza were destroyed

and in Egypt, the New Kingdom fell into disarray

https://en.m.wikipedia.org/wiki/Greek_Dark_Ages