Basically European anti-semitism, culminating in the Holocaust, forced many European Jews to look for another place to live in, away from anti-semitic Europeans; and this in practice involved displacing the people who already lived there. One result was that European anti-semitism got exported to places where for thousands of years Jews and Arabs had got along pretty well, especially compared to what happened in Europe.

Antagonism between Jews and Arabs has the same basic origin as antagonism between settlers in the American West and the native Americans. The fact that Jews and Arabs are very closely related peoples (in many cases essentially identical), and that their religious beiefs and practices are also very closely related, is one of the things that makes this historic tragedy so poignant.