1947/48/49 (those who do not know history are condemned to repeat it)

In 1947, following increasing levels of violence together with unsuccessful efforts to reconcile the Jewish and Arab populations, the British government decided to withdraw from the Palestine Mandate. The UN General Assembly approved the 1947 UN Partition Plan dividing the territory into two states, with the Jewish area consisting of roughly 55% of the land, and the Arab area roughly 45%. Jerusalem was planned to be an international region administered by the UN to avoid conflict over its status.

Immediately following the adoption of the Partition Plan by the UN General Assembly on November 29, 1947, David Ben-Gurion tentatively accepted the partition, while the Arab League rejected it. Attacks on civilians chiefly by Arabs but also by Israelis soon turned into widespread fighting between Arabs and Jews, this civil war being the first "phase" of the 1948 War of Independence.

The State of Israel was proclaimed on May 14, 1948, one day before the expiry of the Palestine Mandate.

Following the State of Israel's establishment, the armies of Egypt, Syria, Jordan, Lebanon, and Iraq joined the fighting and began the second phase of the 1948 Arab-Israeli War. From the north, Syria, Lebanon, and Iraq, were all but stopped relatively close to the borders. Jordanian forces, invading from the east, captured East Jerusalem and laid siege on the city's west. However, forces of the Haganah successfully stopped most invading forces, and Irgun forces halted Egyptian encroachment from the south. At the beginning of June, the UN declared a one-month cease fire during which the Israel Defense Forces were officially formed. After numerous months of war, a cease fire was declared in 1949 and temporary borders, known as the Green Line, were instituted. Israel had gained an additional 26% of the Mandate territory west of the Jordan River. Jordan, for its part, held the large mountainous areas of Judea and Samaria, which became known as the West Bank. Egypt took control of a small strip of land along the coast, which became known as the Gaza Strip.

During and after the war, then Prime Minister David Ben-Gurion set about establishing order by dismantling the Palmach and underground organizations like the Irgun and Lehi. Those two groups were classified as terror organizations after the murder of a Swedish diplomat.

Large numbers of the Arab population fled or were driven out of the newly-created Jewish State. (Estimates of the final refugee count range from 600,000 to 900,000 with the official United Nations count at 711,000.) The continuing conflict between Israel and the Arab world resulted in a lasting displacement that persists to this day.

Immigration of Holocaust survivors and Jewish refugees from Arab lands doubled Israel's population within a year of independence. Over the following decade approximately 600,000 Mizrahi Jews, who fled or were expelled from surrounding Arab countries and Iran, migrated to Israel.