The U.N. General Assembly established the U.N. Relief and Works Agency (UNRWA) in 1949 as a temporary agency focused on relief work for the Palestinians. It began operating in 1950.
Hundreds of thousands of Palestinians became refugees in the war that began when the Palestinians and their Arab allies attacked the fledgling Jewish state the day after its formation in 1948.
Some were purposely flushed from their homes as Jewish forces sought to secure key roads and pacify areas from which Jewish communities had been attacked. Some were encouraged to leave by the Arab states, which told the refugees that they could return shortly to claim the spoils after the Jews were killed. Many simply fled what had become a combat zone.
The Palestinians constituted just one of many refugee populations in the years after World War II, and many outsiders expected their case to be the easiest of the post-war refugee crises to resolve. Many found shelter in neighboring countries that shared their language, religion and culture, and where many of them had blood ties.
The roughly equal number of Jewish refugees who fled or were expelled from the Muslim world during the same period were quickly resettled in Israel or in the West.
Unlike the U.N. High Commission for Refugees (UNHCR), which serves the world's other 19.2 million refugees, UNRWA was not tasked with finding solutions to the refugees' plight.
Instead, UNRWA's definition of refugee -- which counted even migrants who had lived in the area for as little as two years -- further expanded in the 1950s, when, in an unprecedented move, UNRWA included descendants of the original refugees. This was an expanded definition that UNHCR never adopted.
Thus, while other refugee groups have dwindled due to resettlement or death, the Palestinian refugee population, uniquely, continues to grow -- from 914,000 registered refugees in 1950 to about 4.3 million today, roughly one-third of whom live in the West Bank and Gaza Strip.