The main causes of Arab-Israeli conflicts in the twentieth century were:
1. The division of Palestine into separate Jewish and Arab states: This division created tensions between the Jewish and Arab populations in the region, leading to conflicts over land and national identity.
2. Egypt's nationalization of the Suez Canal: This event, which occurred in 1956 under President Gamal Abdel Nasser, led to tensions between Egypt and Israel, as well as other countries like France and Britain. This conflict further exacerbated the Arab-Israeli tensions.
These two factors played significant roles in shaping the Arab-Israeli conflicts in the twentieth century, contributing to the ongoing political, territorial, and ideological disputes in the region.