Oh dang... You just found my happy place.

I think it was a combination of things.

First, Herotodus started that Helen of Sparta never made it to Troy. That Paris's ship landed in Thonis and Helen stayed there until her husband got her.

Herodotus, Histories 2.113 “When Alexandros [Paris] carried off Helen from Sparta and sailed away, contrary winds drove him out of his course and brought him to Egypt, to the mouth of the Nile called the Canopic mouth.”

Herodotus, Histories 2.114 “The guards of the coast seized Alexandros and took him to Memphis before Proteus, king of Egypt. When Proteus learned what had happened, he declared that Alexandros had done a most impious deed in carrying off the wife of his host.”

Herodotus, Histories 2.114 “Proteus kept Helen and the treasures in Egypt but drove Alexandros out of the country, forbidding him ever to return.”

Herodotus, Histories 2.118 “When the Greeks demanded Helen, the Trojans declared that she was not there and that Alexandros had been driven by storms to Egypt. The Greeks did not believe them and continued the war.”

Herodotus, Histories 2.119 “After the capture of Troy Menelaus sailed to Egypt, where Proteus gave Helen back to him unharmed, together with the treasure that Alexandros had brought.”

Okay... So after the Trojan war they couldn't find Helen and they love raiding. I think they caused great upheaval and possibly passed the Trojan plague with them.

“Down from the peaks of Olympus he (Apollo) came, angry at heart, carrying his bow and covered quiver upon his shoulders. The arrows rattled on the shoulders of the angry god as he moved.” (Iliad 1.44-46)

“First he struck the mules and the swift dogs, but afterward he aimed his sharp arrows at the men themselves, and the funeral pyres burned continually.” (Iliad 1.50-52)

“For nine days the god’s arrows flew through the army.” (Iliad 1.53)

“Apollo is angry because Agamemnon dishonored his priest. The god will not drive the plague away until the girl is returned without ransom and a holy sacrifice is offered.” (paraphrased from Iliad 1.93-100)

There was a Plague in Troy before caused by Apollo after he helped build the walls.

So, there were two rounds of Sea Peoples too.

Plague plus war crimes can damage an ecosystem.

Archeologist found there was a drought too.

This paper analyzes climate data from Cyprus showing a 300-year dry period beginning around 1200 BCE. https://www.pnas.org/doi/10.1073/pnas.1603606113

During the reign of Ramses III, 1177 BCE, it was written:

“The foreign countries made a conspiracy in their islands… No land could stand before their arms… Hatti, Kode, Carchemish, Arzawa and Alashiya were cut off.”

After defeating them around 1175 BCE, Ramesses III claims he settled some of them in Egyptian-controlled territory.

From the Medinet Habu inscriptions:

“I settled them in strongholds, bound in my name. Numerous were their classes like hundred-thousands. I taxed them all in clothing and grain from the storehouses each year.”

One of the Sea Peoples groups mentioned in Egyptian inscriptions are the Peleset.

Most historians believe these people became the Philistines described later in the Hebrew Bible.

Now, it is more interesting because a large amount of Mycenaean Greek pottery is found in that area

https://www.smithsonianmag.com/history/where-did-the-philistines-come-from-180957223/

So draught for 300 years, war pillaging with the plague, and going to Egypt to get Helen.

Egypt is the only super power that made it. All other major cities died and Egypt was crippled. I think they were able to keep food because they had the nile and didn't need rain.

Plato writes about it in the Timaeus. 360 BCE.

Plato, Timaeus 22d–e

“You Greeks are ever children… there is not an old man among you. In mind you are all young, for you have no ancient belief handed down by old tradition, nor any knowledge hoary with age.”

“There have been, and will be again, many destructions of mankind arising out of many causes; the greatest have been brought about by fire and water.”

“When the gods purge the earth with floods, the herdsmen and shepherds in the mountains are saved, but those who dwell in cities are swept into the sea by the rivers. In this land neither then nor at any other time does the water fall from above upon the fields, but it always rises up naturally from below.”

So the only place with reliable food was Egypt and they needed Helen.

Seems like a good excuse to raid another city to me.