Time and again, the argument is heard that the Palestinians lived in the land of Israel for many centuries as a homogeneous people—until the advent of Zionism, after which they were subject to expulsions, oppression, and occupation. But, notes Yoram Ettinger, in the pre-state era the Arab and Muslim population was in fact highly heterogeneous, and composed to a large degree of immigrants and their descendants:
[For instance], between 1880 and 1919, Haifa’s Arab population surged from 6,000 to 80,000, mostly due to migrant workers. The eruption of World War II accelerated the demand for Arab manpower by the British Mandate’s military and civilian authorities. Moreover, Arab migrant workers were imported by the Ottoman empire, and then by the British administration, to work in major civilian and military infrastructure projects. Legal and illegal Arab migrants were also attracted by economic growth, which was generated by the Jewish community beginning in 1882.
According to a 1937 report by the British Peel Commission, from “1922 through 1931, the increase of Arab population in the mixed-towns of Haifa, Jaffa, and Jerusalem was 86 percent, 62 percent, and 37 percent respectively, while in purely Arab towns such as Nablus and Hebron it was only 7 percent, [with] a decrease of 2 percent in Gaza.”
Read more on Ettinger Report : http://theettingerreport.com/Palestinian-Issue/Who-were-the-1948-Arab-refugees-.aspx