The First Arab-Israeli War (30 November 1947-20 July 1949), was a war fought between Israel and the neighboring Arab League states. The war was caused by the division of Mandatory Palestine between a Jewish state and an Arab state, with the Jewish state proclaiming independence as the state of Israel. The surrounding Arab countries refused to recognize Israel's independence and invaded from all sides, but poor leadership among the numerically-superior Arab armies led to Israel defeating all invasions, crushing the Arab League's "Arab Liberation Army" and the Palestinian Holy War Army, and annexing several lands that were designated as Arab lands under the United Nations partition plan. The 29 November 1947 adoption of the UN Partition Plan led to sectarian violence between Jews and Arabs in the British-ruled region of Palestine, with the Jewish Haganah, Palmach, Irgun, and Lehi militias fighting against the Arab Holy War Army, the Arab Liberation Army, and Transjordan's Arab Legion. Britain ordered for its soldiers to withdraw from the region as the violence escalated, and it rarely intervened in the conflict, which became known as the Palestinian Civil War. The result of this conflict was the exodus of Arabs from Palestine and the expulsion of Jews from the Arab countries, leading to increased Jewish immigration in Israel and increased Palestinian emigration to the other Arab states and to the West.
On 14 May 1948, Mandatory Palestine expired, leading to the Jews proclaiming the independence of the new state of Israel. The surrounding Arab states of Egypt, Transjordan, Iraq, and Syria, among others, invaded what had just ceased to be Mandatory Palestine, starting the second phase of the conflict: the Arab-Israeli War. The first ten months of fighting took place mostly in Palestine and for a short time also in the Sinai Peninsula and southern Lebanon. The Arab forces had a decentralized command, and their forces were poorly-experienced; the Israelis benefited from assistance from foreign volunteers such as Mickey Marcus, and they were able to hold off the Arab invasions. In 1949, the Israelis began to push the Arabs out of their own territory, advancing into the Galilee and Jerusalem. On 20 July 1949, a ceasefire was called between Israel and the Arab League. Israel maintained its de facto independence (although its Arab neighbors refused to recognize it), and Israel annexed the Galilee, Jaffa, Lydda, Ramla, parts of the Negev, the Tel Aviv-Jerusalem road, West Jerusalem, and parts of the West Bank. While Egypt and Jordan were considered to have lost the war, they also had territorial gains, with Egypt occupying the Gaza Strip and Jordan occupying the rest of the West Bank. The Israeli War of Independence was the start of the Arab-Israeli Conflict, which would continue into the 21st century as Israel continued to protect its territorial integrity from its Arab neighbors. It was also one of the most important chapters of the Israeli-Palestinian conflict, as the Palestinian Nakba (exodus) led to animosity being created between the two nations. The war would lead to nearly a century of Palestinian terrorism, guerrilla warfare, and political campaigning with the goal of creating an independent Palestine, and Israel would have to fight against the Palestinian terrorist threat for decades as thousands of lives were lost on both sides.