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The Philistines settled in the present Gaza area, in a territory slightly larger than the Gaza strip, including a few coastal towns in present Israel near Gaza.
They inhabited five towns in all, and never settled in Judaea or Galilee, although they did attempt to exert authority there.
Historians are not clear on what became of the Philistines, as they eventually disappear from history.
But one good idea is to consult the history of Judea and surrounding areas in the days of the Roman and Bizantine Empires, and perhaps even earlier during the Hellenistic period commencing with Alexander the Great:
if the Philistines are not mentioned anywhere in these epochs, then they had already disappeared from that area as a distinct people.
For example, they could have been exiled by the Assyrians or the Babylonians and settled elsewhere, as was with the ten tribes of Northern Israel (Assyria) and the Judeans (Babylonia).
Or they may have amalgamated with other populations.
In the southern Negev lived the Idumeans, also called Edomites. And there were, as already mentioned, the Samaritans, who lived between Judea and Galilee. There were also Greek settlers, and some Romans.
The idea that everyone was an Arab in historical Israel, or Palestine, is erroneous. There were no Arabs living there before 634 AD, and when they arrived, they were a minority.
In 1870 AD, the Arabs were 7.5% (seven and a half percent) of the population of Jerusalem. The Jews were by far the largest population, long, long before the 1919 Palestine mandate of the British (The League of Nations mandate).
The various Christians were the second largest population in Jerusalem.
The Crusades also deserve a mention, together with the Arab and Turkish conquests. A number of conquests brought about great changes in society in Palestine, or Israel.
For example, the last Muslim leader to conquer the area from the Western Christians who had settled there, after arriving from Egypt with a large army, deliberately made the land become desolate, so as to prevent another crusade and another wave of Christian settlers from the West.
In so doing, he made the land barren both for Christians and Muslims.