"the Arab claim that an indigenous Arab population was displaced by Jewish immigrants"
In 1948, there were approx. 500,000 Arabs living in the area mandated to the Jewish people, and about 90,000 Jews. At that point, the Arabs had the choice of remaining in a state without political rights, or applying for entry into a newly-mandated Arab nation. If I'm not mistaken, the refugee camps comprise precisely that: refugees who made a choice not to remain, and who took a gamble that they would be taken in by their Arab brothers and sisters, which they were not. Instead, the 'host' countries 'maintain' the camps rather than integrating the people into their (Arab) population.
Have you read Joan's book?
The last population survey by the Brits in 1947 estimated 1.1 million Arabs and about 650,000 Jews in the entire mandate area. The area allocated to Israel by the UN was majority Jewish. I'm not sure anyone has a good handle on population, since Jewish immigration was booming.
If I'm not mistaken, the refugee camps comprise precisely that: refugees who made a choice not to remain, and who took a gamble that they would be taken in by their Arab brothers and sisters...
They also expected to follow victorious Arab armies back, where they could take their Jewish neighbors homes and proberty, the deceased Jews no longer needing them. Didn't work out that way.