Tarik, you err and let's see how. Starting point understood as British Mandate area means that closely 80 percent of the land is in Arab hands - and more than 3000 years old continuum of Jewish presence in the East Bank was abruptly ended. If some people, then the Jewish ones, were and are the indigenous people. First Arabs came as intruders along post-Muhammad conquests. You should know that there was a vast influx of Arabs from as far as maghreb states and Sudan, not to mention the neighbouring countries to modern days Israeli area due to the higher living standard. These vast numbers of people are of Arab origin, but, are they "Palestinians", is another question. War 1948: most Arabs moved away due to the command of the coming Arab armies command and due to the "fact" they would soon come back to take what would be left from the Jewish property. So didn't it happen. These Arabs were not expelled by the Jews, but, by exhortation of their Arab brethren.
from the article: Pro-Mideast in America: Getting past 'Pro-Israel' and 'Pro-Palestine'