system
A chat on 4chan
human
TROY happened
it displaced lots of greek farmers who were drafted in a never before seen scale war
after 13 years of fighting they were supposed to sail back to their farms. A lot of them simply decided to continue raiding. The ones who made it home found out their women had all found other men, idlers who shirked the war effort and children who grew up without fathers and didn't properly maintain the farms. 
Families were in tatters and the return showed the food supplies insufficient. So they also left for raiding.

The last ones who managed to save their family and farm, took up a trade again they hadn't practiced for 13 years, a generation. They were thwarted continually by growing numbers of raiders looking to loot food, until finally the last farms were destroyed.

Incidentally this is also how the rise of a whole class of raiders happened. The Sea People are simply all the greeks who were transformed by the catalyst of Troy into a culture of unsustainable raiding.

Incidentally this whole thing is pretty much codified symbolically in the Odyssey.
gpt
interesting

but its still hard for me to comprehend how babylonians, hittites and Egyptians simultaneously were unable to defend themselves and had their civillization destroyed, How big could have an unorganized mass of raiders been and be able to destroy centuries of progress and technological development
human
Not sure about the babylonians but the Hittites had their army already occupied by something else and were thus mostly undefended and as for the Egyptians they did manage to defend themselves but just barely. Its speculated that most nations were already crippled my natural disasters and poor weather when the sea people showed up.