The collapse of Mycenaean Civilization, when all major Mycenaean regional centres fell out of use after suffering a combination of destruction and abandonment.

The Greek Dark Age

Explanation:

The Late Bronze Age collapse, sometimes referred to as the Age of Calamities, was a phase in the Aegean Region, Eastern Mediterranean, and Southwestern Asia. It occurred during the course of the Late Bronze Age to the Early Iron Age. A lot of historians consider the phase as somewhat aggressive, swift, and culturally destructive.

Majority of the historians characterised the fall of the Mycenaeans, and the entire Bronze Age fall, to climatic or environmental disaster followed by an intrusion by the Dorians (or Sea Peoples). Some referred to the huge presence of edged iron weapons as a causative cause. But yet no certain explanation best suits all evidenced of archaeology in giving clarity to the fall of the Mycenaean culture.

Not a single one of the Mycenaean palaces of the Late Bronze Age scaled through, with the likely exclusion of the Cyclopean stronghold on the Acropolis of Athens which infers to major depopulation.

In the period of the Dark Ages, Greece seems to be grouped into independent regions based on kinship sets, and the oikoi, or households.