> The League of Nations gave Britain mandatory power over Palestine in 1922. British rule and Arab efforts to prevent Jewish migration led to growing violence between Arabs and Jews, causing the British to announce its intention to terminate the Mandate in 1947. The UN General Assembly recommended partitioning Palestine into two states: Arab and Jewish. However, the situation deteriorated into a civil war. The Arabs rejected the Partition Plan, the Jews ostensibly accepted it, declaring the independence of the State of Israel in May 1948 upon the end of the British mandate. Nearby Arab countries invaded Palestine, Israel not only prevailed, but conquered more territory than envisioned by the Partition Plan. During the war, 700,000, or about 80% of all Palestinians fled or were driven out of territory Israel conquered and were not allowed to return, an event known as the Nakba (Arabic for 'catastrophe') to Palestinians. Starting in the late 1940s and continuing for decades, about 850,000 Jews from the Arab world immigrated ("made Aliyah") to Israel.

https://en.wikipedia.org/wiki/History_of_Palestine