The Arab-Israeli War of 1948 broke out when five Arab nations invaded territory in the former Palestinian mandate immediately following the announcement of the independence of the state of Israel on May 14, 1948.
Fighting began with attacks by irregular bands of Palestinian Arabs attached to local units of the Arab Liberation Army composed of volunteers from Palestine and neighboring Arab countries. These groups launched their attacks against Jewish cities, settlements, and armed forces.
The goal of the Arabs was initially to block the Partition Resolution and to prevent the establishment of the Jewish state.
After Israel declared its independence on May 14, 1948, the fighting intensified with other Arab forces joining the Palestinian Arabs in attacking territory in the former Palestinian mandate. On the eve of May 14, the Arabs launched an air attack on Tel Aviv, which the Israelis resisted. This action was followed by the invasion of the former Palestinian mandate by Arab armies from Lebanon, Syria, Iraq, and Egypt. Saudi Arabia sent a formation that fought under the Egyptian command.
Office of the Historian - Milestones - 1945-1952 - The Arab-Israeli War of 1948