The international forces that were guaranteeing the safety of Palestinian refugees following Israel's 1982 Invasion of Lebanon leave Beirut. Five days later, several thousand refugees are massacred in the Sabra and Shatila refugee camps by Phalange forces.

In 1949, UNRWA formally defined the term "Palestine refugee" to refer to any Palestinian citizen or the descendant of any male Palestinian citizen who—if their regular place of residence was located within Mandatory Palestine between 1 June 1946 and 15 May 1948—was found to have "lost both home and means of livelihood" during the 1948 Palestine war. While this definition originally included Arab Palestinians displaced from or within Israel as well as Jewish Palestinians displaced from Arab-controlled territory, it ceased to apply to Arabs and Jews who became Israeli citizens in 1952; Arab Palestinians who were displaced from their homes while ultimately remaining within Israeli territory were instead designated as "present absentees" and not subject to UNRWA's jurisdiction. In addition to more than 700,000 Palestinians who fled or were expelled by Israel before the 1949 Armistice Agreements, another 285,000 to 325,000 Palestinians were displaced due to the 1967 Arab–Israeli War.