Why were the Palestinians who fled the fighting during the 1948 war not allowed to return to their homes afterwards Would doing so have prevented the Palestinian refugee issue we see today ?
Israel prevents Palestinian refugees from returning because it claims they are a security threat. However, seeing as Israel is a settler colony built on stolen land, it did not have the population numbers to sustain itself. It could only be established by creating new demographic realities on the ground, these new realities necessitated that approximately 80% of the Palestinians in what is today considered Israel be ethnically cleansed to maintain a demographically stable Zionist ethnocracy. In short, Israel can only exist because millions of Palestinians are scattered refugees all over the world, simply because they are not Jewish.
The answer for your second question is yes.
Palestinian refugees line up for food at a camp in Amman, Jordan in 1955.