What were those shocks?

Drought is the most recently and powerfully documented.

Paleoclimatological research — using sediment cores from lakes and sea beds, pollen records, speleothem (cave formation) isotope analysis, and other proxies — has established that the eastern Mediterranean experienced a prolonged and severe drought beginning around 1200 BCE.

The research of Brandon Drake and others has shown that rainfall dropped significantly across the Levant, Anatolia, and the Aegean during exactly the period of the collapse.

Crop failures, famine, and population stress would have been the predictable results.