Causes of the 1948 Palestinian expulsion and flight
During the 1948 Palestine war in which the State of Israel was established, around 700,000 Palestinian Arabs, or 85% of the total population of the territory Israel captured, were expelled or fled from their homes. The causes of this mass displacement have been a matter of dispute, though today most scholars consider that the majority of Palestinians were directly expelled or else fled due to fear.
Source: Wikipedia — Causes of the 1948 Palestinian expulsion and flight (CC BY-SA 4.0)