Western civilization almost completely disintegrated around 1200bc, some say 1177bc. The Greeks actually forgot how to write and it was 4 centuries before they became literate again. The high cultures of the Minoans, Hittites, Mycenaeans, Trojans, Cypriats, Ugarites, Amorites disappeared. And even Egypt was knocked to its knees.
There are dozens of proposed explanations but they are all fragmentary and fall short of explaining the totality of the cultural disintegration.