If they were not there, then where did they come from and how did it get so big in the course of fifty years or so?
They came mainly from Syria, I believe. And they got a big population because Syria wouldn't let them come home.
Still won't.
They flocked in once the place started to become prosperous. The same thing happened in Algeria, after the French brought modernism and better agriculture, etc. (all the things Islam disparaged).
Most of today’s Gaza residents are Egyptians who were trying to flee back to Egypt in 1948 and were caught, and stuck, in the Gaza when Egypt wouldn’t let them back in.
Most of them came from Egypt /Syria/Jordan /Saudi Arabia for the work after the Jews started to prosper.
Arab Palestinian leaders:
Yasser Arafat was born August 24, 1929 in Cairo, Egypt
Saeb BERAKAT , Was born on April 28, 1955, in Jordan.
Faisal Abdel Qader Al-Husseini was born in Baghdad in1948 Iraq.
Sari Nusseibeh, was born in 1949 in Damascus, Syria.
Mahmoud al-Zahar, was born in 1945 in Cairo, Egypt.
http://israelseen.com/2014/02/06/which-israeli-and-palestinian-leaders-were-born-in-palestine/