system
A chat on 4chan
human
They likely did as the Romans did and cut down all of their forests until they needed to import natural resources, and grew their population until the land could not support them and the economy collapsed. After a famine caused by multiple years of drought, the seafaring states sent large chunks of their populations out on boats to go conquering other lands.

As for who the Sea Peoples were, I believe the Greeks were one of them. King Pelops came from what is now Turkey and took over southern Greece which became known as Pelops's Island, the Peloponnesus. His people in Greece would have had good relations with the mother country in Asia Minor. You had an alliance of seafaring peoples who would have been known to the Egyptians as the Sea Peoples from the north, the people of PLPS -- easily misheard or lazily pronounced as PLS, the Peleshet.

The island of Sardinia was filled with small fortresses known as Nuraghi. No one today knows anything about this Nuragic civilization, but they clearly had a well developed culture and a good enough economy to need to build fortresses. The island is positioned to control trade between the western and eastern Mediterranean. We know that this trade existed because British tin has been found in the Levant. Tin is needed to make bronze, so it would have been valuable to everyone in the Bronze Age. The Sardianians could have been the Sherdan of the Sea Peoples. The Sekles could have been the Sicels of Sicily. The Luka and Denyen could have been Italy's Ligurians and Daunians, but there are other candidates on Asia Minor that are equally or more likely. And the Libyan tribes of the Sea Peoples would have been the trading partners of Sardinia and Sicily.

So with their crops failing, they all get together and decide to invade a well known place that has fertile soil replenished annually by the Nile River. The Egyptians defeat them.
gpt
Then all hell breaks loose and nobody knows what happened, but all of the countries that launched these fleets had their well-fortified cities invaded and burned by unknown armies that wanted to destroy them rather than capture their resources. These might have been each others' war fleets, and there might have been a land invasion of Greece by the Dacians. I'm guessing that the attackers used trebuchets to launch a form of Greek Fire, early napalm over the city walls. The Trojan Horse could have been a literary allusion to trebuchets left in the field by the Greek army when they abandoned the siege.

Tyre escapes the destruction and is therefore a likely candidate for the evil mastermind attacking everyone's cities while their armies were away. And with their trading partners gone, the central and western Mediterranean civilizations collapsed into a dark age and disappeared from history until the Romans got uppity. The Peleshet settled on the Levantine coast and became known as the Philistines, a people merged with the Canaanite tribes but distinct from them.

At the same time as the Bronze Age collapse, the Hittites developed iron weapons which threatened to make bronze weapons obsolete. This would have undermined the tin trade which was a source of trading empires' wealth. It is unclear if this had an effect or not. The Hittite weapons were early in development and may not have been widely used or traded.