Palestinians are an Arab people, whose traditions, history and ethinicity is centered on land formerlly in the British Mandate of Palestine; i.e. present-day Israel, the Occupied Palestinian Territories (West Bank and Gaza). Palestinians are mostly Muslim, but there are many who are from Palestine and are Christian as well.
The wave of Palestinian refugees created after the creation of the State of Israel was caused in part by surrounding Arab nations, and in part by the creation of the state of Israel. In any case these refugees have never been allowed to return to their homes, and properties (many homes and properties have been expropriated from the refugees, by the state of Israel).
There can be no doubt that many fled in terror from war, whether they were misled to leave, with the expectation of return, or with the expectation of victory, these people have never been allowed to return.
At midnight on 14 May 1948, when the last British soldiers were departing and the new state was proclaimed, the Zionists had captured the the Arab quarters of west Jerusalem and infiltrated the old city; they had taken Jaffa and opened a corridor between the coasts and Jerusalem; and they had destroyed dozens of Arab villages. In early April their most well publicized crime had been committed: the massacre of 254 civillians of Deir Yassin.