The 1948 (or First) ArabIsraeli War was the second and final stage of the 19471949 Palestine war. It formally began following the end of the British Mandate for Palestine at midnight on 14 May 1948; the Israeli Declaration of Independence had been issued earlier that day, and a military coalition of Arab states entered the territory of British Palestine in the morning of 15 May.

The first deaths of the 19471949 Palestine war occurred on 30 November 1947 during an ambush of two buses carrying Jews. There had been tension and conflict between the Arabs and the Jews, and between each of them and the British forces since the 1917 Balfour Declaration and the 1920 creation of the British Mandate of Palestine. British policies dissatisfied both Arabs and Jews. Arab opposition developed into the 19361939 Arab revolt in Palestine, while the Jewish opposition developed into the 19441947 Jewish insurgency in Palestine. In 1947, these ongoing tensions erupted into civil war following the 29 November 1947 adoption of the United Nations Partition Plan for Palestine, which planned to divide Palestine into an Arab state, a Jewish state, and the Special International Regime encompassing the cities of Jerusalem and Bethlehem.

On 15 May 1948, the civil war transformed into a conflict between Israel and the Arab states following the Israeli Declaration of Independence the previous day. Egypt, Transjordan, Syria, and expeditionary forces from Iraq entered Palestine. The invading forces took control of the Arab areas and immediately attacked Israeli forces and several Jewish settlements. The 10 months of fighting took place mostly on the territory of the British Mandate and in the Sinai Peninsula and southern Lebanon, interrupted by several truce periods.As a result of the war, the State of Israel controlled the area that the UN had proposed for the Jewish state, as well as almost 60% of the area proposed for the Arab state, including the Jaffa, Lydda, and Ramle area, Galilee, some parts of the Negev, a wide strip along the Tel AvivJerusalem road, and some territories in the West Bank. Israel also took control of West Jerusalem, which was meant to be part of an international zone for Jerusalem and its environs. Transjordan took control of East Jerusalem and the remainder of the former British mandate, annexing it the following year, and the Egyptian military took control of the Gaza Strip. At the Jericho Conference on 1 December 1948, 2,000 Palestinian delegates called for unification of Palestine and Transjordan as a step toward full Arab unity. The conflict triggered significant demographic change throughout the Middle East. Around 700,000 Palestinian Arabs fled or were expelled from their homes in the area that became Israel, and they became Palestinian refugees in what they refer to as the Nakba ("the catastrophe"). In the three years following the war, about 700,000 Jews emigrated to Israel. Around 260,000 Jews moved to Israel from the Arab world during and immediately after the war.

Mandatory Palestine (Arabic: فلسطين Filasṭīn; Hebrew: פָּלֶשְׂתִּינָה (א"י) Pālēśtīnā (E.Y.), where "E.Y." indicates Ērētz Yīśrā'ēl, the Land of Israel) was a geopolitical entity established between 1920 and 1948 in the region of Palestine under the terms of the League of Nations Mandate for Palestine.

During the First World War (1914–1918), an Arab uprising against Ottoman rule and the British Empire's Egyptian Expeditionary Force under General Edmund Allenby drove the Turks out of the Levant during the Sinai and Palestine Campaign. The United Kingdom had agreed in the McMahon–Hussein Correspondence that it would honour Arab independence if they revolted against the Ottomans, but the two sides had different interpretations of this agreement, and in the end, the UK and France divided up the area under the Sykes–Picot Agreement – an act of betrayal in the eyes of the Arabs.

Further complicating the issue was the Balfour Declaration of 1917, promising British support for a Jewish "national home" in Palestine. At the war's end the British and French set up a joint "Occupied Enemy Territory Administration" in what had been Ottoman Syria. The British achieved legitimacy for their continued control by obtaining a mandate from the League of Nations in June 1922. The formal objective of the League of Nations mandate system was to administer parts of the defunct Ottoman Empire, which had been in control of most of the Middle East since the 16th century, "until such time as they are able to stand alone".During the Mandate, the area saw the rise of nationalist movements in both the Jewish and Arab communities. Competing interests of the two populations led to the 1936–1939 Arab revolt in Palestine and the 1944–1948 Jewish insurgency in Mandatory Palestine. After the failure of the Arab population to accept the United Nations Partition Plan for Palestine, the 1947–1949 Palestine war ended with the territory of Mandatory Palestine divided among the State of Israel, the Hashemite Kingdom of Jordan, which annexed territory on the West Bank of the Jordan River, and the Kingdom of Egypt, which established the "All-Palestine Protectorate" in the Gaza Strip.