The State of Israel, the first Jewish state for nearly 2,000 years, was proclaimed at 1600 on 14 May 1948 in Tel Aviv. The declaration came into effect the following day as the last British troops withdrew. Palestinians remember 15 May as "al-Nakba", or the Catastrophe.

The year had begun with Jewish and Arab armies each staging attacks on territory held by the other side. Jewish forces, backed by the Irgun and Lehi militant groups made more progress, seizing areas alloted to the Jewish state but also conquering substantial territories allocated for the Palestinian one.

Irgun and Lehi massacred scores of inhabitants of the village of Deir Yassin near Jerusalem on 9 April. Word of the massacre spread terror among Palestinians and hundreds of thousands fled to Lebanon, Egypt and the area now known as the West Bank.

The Jewish armies were victorious in the Negev, Galilee, West Jerusalem and much of the coastal plain.

The day after the state of Israel was declared five Arab armies from Jordan, Egypt, Lebanon, Syria and Iraq immediately invaded Israel but were repulsed, and the Israeli army crushed pockets of resistance. Armistices established Israel's borders on the frontier of most of the earlier British Mandate Palestine.

Egypt kept the Gaza Strip while Jordan annexed the area around East Jerusalem and the land now known as the West Bank. These territories made up about 25% of the total area of British Mandate Palestine.