During the 1948 Palestine war in which the State of Israel was established, around 700,000The exact number of refugees is unknown. See List of estimates of the 1948 Palestinian expulsion and flight for details. Palestinian Arabs, or 85% of the total population of the territory Israel captured, were expelled or fled from their homes. The causes of this mass displacement have been a matter of dispute, though today most scholars consider that the majority of Palestinians were directly expelled or else fled due to fear.

Causes of the exodus include direct expulsions by Israeli forces, destruction of Arab villages, psychological warfare including terrorism, dozens of massacres which caused many to flee out of fear, such as the widely publicized Deir Yassin massacre, crop burning,: "While before May, burning Arab crops was mainly a Haganah means of retaliation for Arab attacks, during May–June the destruction of the fields hardened into a set policy designed to demoralise the villagers, hurt them economically and, perhaps, precipitate their exodus." typhoid epidemics in some areas caused by Israeli well-poisoning, and the collapse of Palestinian leadership including the demoralizing impact of wealthier classes fleeing. Many historians consider that the events of 1948 were an instance of ethnic cleansing.

Violence and psychological warfare Zionist forces used violence and psychological warfare that initiated, accelerated and increased the Palestinian exodus. Dozens of massacres targeting Arabs were conducted by Israeli military forces and between 400 and 600 Palestinian villages were destroyed.

According to historian Benny Morris, during the exodus of Haifa "The Haganah broadcasts called on the populace to 'evacuate the women, the children and the old immediately, and send them to a safe haven.'"Morris 2004, p. 191. In his conclusions concerning the second wave of the flight, Morris also cites the atrocity factor as one of the causes, referring to the Deir Yassin massacre and how its widespread broadcast on Arab radio stations undermined Arabs' morale.Benny Morris, The Birth of the Palestinian refugee problem revisited, p. 264. Historian Yoav Gelber also considers that the "Haganah, IZL and LHI's retaliations terrified the Arabs and hastened the flight".Yoav Gelber, Palestine 1948, p. 76.

Biological warfare was waged against Palestinians in Operation Cast Thy Bread. On March 17 1948, the Irgun made an Arabic-language broadcast, warning urban Arabs that "typhus, cholera and similar diseases would break out heavily among them in April and May".Erskine Childers, "The Other Exodus" in Laqueur, p. 184.

In their volume on the 1947–1948 period in Jerusalem and surrounding areas, O Jerusalem!, Larry Collins and Dominique Lapierre give a variety of explanations for the cause of the 1948 Palestinian exodus, but conclude, "Above all, fear and uncertainty fueled the Arabs' flight."Collins, Larry and Dominique Lapierre. O Jerusalem! New York: Simon and Schuster, 1972. p. 337. Middle East historian Karen Armstrong described a similar mechanism.Armstrong, Karen. Jerusalem: One City, Three Faiths. New York: Ballantine Books, 1996. pp. 389–390.

Erskine Childers, while dismissing the fact that Arab leaders instigated the flight on radio broadcasts, points out that Zionist radio broadcasts were designed to demoralize the Arab audience.Childers: The Wordless Wish, p. 188. On Zionist radio broadcasts from mid-April through mid-May and compared to Arab radio broadcasts urging calm and warning against flight. The author cites the fact that rumours were spread by the Israeli forces that they possessed the atomic bomb.Childers: The Wordless Wish, p. 187. Historian Rashid Khalidi similarly points to what he describes as the Zionist "psychological offensive" which was highlighted by, though not limited to, radio messages warning the Arabs of diseases, the ineffectiveness of armed resistance and the incompetence of their leaders.Khalidi, W.(1959): "Why Did The Palestinians Leave?", Middle East Forum, vol. XXXV, no. 7, pp. 21–24. Cited by Glazer (1980), p. 101.

According to historian Ilan Pappé, the Haganah engaged in what it called "violent reconnaissance", in which "[s]pecial units of the Haganah would enter villages looking for 'infiltrators' ... and distribute leaflets warning the people against cooperating with the Arab Liberation Army. Any resistance to such an incursion usually ended with the Jewish troops firing at random and killing several villagers."Pappé, pp. 55, 56. Khalidi mentions "repeated and merciless raids against sleeping villages carried out in conformity with plan C", i.e. in the period before April 1948.

Various authors give examples of instigation of whisper campaigns. Childers cites the fact that rumours were spread by the Israeli forces that they possessed the atomic bomb. Morris cites Yigal Allon, the Palmach commander, describing such a campaign: "I gathered the Jewish mukhtars, who had ties with the different Arab villages, and I asked them to whisper in the ears of several Arabs that giant Jewish reinforcements had reached the Galilee and were about to clean out the villages of the Hula, [and] to advise them, as friends, to flee while they could. And the rumour spread throughout the Hula that the time had come to flee. The flight encompassed tens of thousands. The stratagem fully achieved its objective."Morris 2004, p. 251.

Shelling of civilians Khalidi illustrates the psychological warfare of the Haganah by the use of the Davidka mortar. He writes that it was a "the Zionists favorite weapon", which they used against civilians: "the Davidka tossed a shell containing 60 lbs. of TNT usually into crowded built-up civilian quarters where the noise and blast maddened women and children into a frenzy of fear and panic."

Various authors mention specific cases in which the Yishuv engaged in shelling of civilians: Morris says that during the battle of Tiberias the Haganah engaged in bombarding the Arab population with mortars Morris says that during the exodus of Haifa a primary aim of mortar barrages was demoralisation: "The Haganah mortar attacks of 21–22 April were primarily designed to break Arab morale in order to bring about a swift collapse of resistance and speedy surrender.... But clearly the offensive, and especially the mortarring, precipitated the exodus. The three inch mortars 'opened up on the market square [where there was] a great crowd ... a great panic took hold. The multitude burst into the port, pushed aside the policemen, charged the boats and began to flee the town', as the official Haganah history later put it." Nathan Krystall writes: "As a precursor to its attack on Qatamon, the Zionist forces subjected the neighborhood to weeks of heavy artillery shelling. On 22 April, the Arab National Committee of Jerusalem ordered its local branches to relocate all women, children, and elderly people from the neighborhood." In his report concerning the fall of Jaffa the local Arab military commander, Michel Issa, writes: "Continuous shelling with mortars of the city by Jews for four days, beginning 25 April, ... caused inhabitants of city, unaccustomed to such bombardment, to panic and flee." According to Morris the shelling was done by the Irgun. Their objective was "to prevent constant military traffic in the city, to break the spirit of the enemy troops [and] to cause chaos among the civilian population in order to create a mass flight".. High Commissioner Cunningham wrote a few days later "It should be made clear that IZL attack with mortars was indiscriminate and designed to create panic among the civilian inhabitants."

Massacres

Dozens of massacres were committed against Palestinians during the war, including the Balad al-Shaykh massacre 31 Dec 1947, Sasa massacre 15 Feb 1948, Deir Yassin massacre 9 Apr 1948, Ein al-Zeitun massacre 1 May 1948, Abu Shusha massacre, Tantura massacre 23 May 1948, Lydda massacre 12 July 1948, Dawayima massacre 29 Oct 1948, and the Safsaf massacre 29 Oct 1948.

In his memoirs the Palestinian Arab physician Elias Srouji claims massacres were intended to scare inhabitants. He wrote: Tactics became even more brutal when the Zionists were ready to complete their occupation of the Galilee in October. By that time the Arab villagers, having seen what had happened elsewhere, had become adamant about staying put in their homes and on their lands. To frighten them away, the occupying forces started a strategy of planned massacres, which were carried out in Eilabun, Faradiyya, Safsaf, Sa'sa', and other villages. In places where this was not to their advantage for one reason or another, the army would resort to forceful expulsion. I was to witness some of these tactics in Rameh a month or so later.Elias Srouji, "The Last Days of 'Free Galilee': Memories of 1948", J. Palestine Studies, 33(1), pp. 55–67.

Nathan Krystall writes: News of the attack on and massacre in Deir Yassin spread quickly throughout Palestine. De Reynier argued that the "general terror" was "astutely fostered by the Jews, with Haganah radio incessantly repeating 'Remember Deir Yassin' and loudspeaker vans broadcasting messages in Arabic such as: 'Unless you leave your homes, the fate of Deir Yassin will be your fate.'"

According to historian Simha Flapan, "from another perspective, [the Deir Yassin massacre] made perfect sense. More panic was sown among the Arab population by this operation than by anything that had happened up to then.... While Ben-Gurion condemned the massacre in no uncertain terms, he did nothing to curb the independent actions of the Jewish underground armies."

Historiography Scholarship today generally considers that violence and direct expulsions perpetrated by Zionist forces throughout both phases of the 1947–1949 Palestine war (both during the civil war phase and during the 1948–1949 Arab–Israeli war) were the primary cause of the displacement of the Palestinians. Many historians consider that the events of 1948 fit the definition of ethnic cleansing.

In a review of scholarship on the topic, Jerome Slater asserted that the New Historians had decisively refuted "the conventional Zionist-Israeli mythology" that most of the 700,000 Palestinian Arabs had "fled" voluntarily. The "mythology" held that until the Arab states invaded Palestine to begin the 1948 Arab–Israeli War that the Zionist forces had attempted to demonstrate a willingness to coexist and attempted to keep the Arabs to stay. The New Historians have however established this to be false, and that "well before the Arab invasion some 300,000 to 400,000 Palestinians (out of a population of about 900,000 at the time of the UN partition) were either forcibly expelled—sometimes by forced marches with only the clothes on their backs—or fled as a result of Israeli psychological warfare, economic pressures, and violence, designed to empty the area that would become Israel of most of its Arab inhabitants." Rather than the Arab invasion being responsible for the flight of the Palestinian Arabs, Walid Khalidi wrote that: "It was not the entry of the Arab armies that caused the exodus. It was the exodus that caused the entry of the Arab armies." Massacres and forced expulsions of Palestinian Arabs by Zionist forces were either tolerated or implemented by the Yishuv leadership, with Yitzhak Rabin reporting on the orders he received in the expulsion of 50,000–70,000 Palestinians from Lydda and Ramle that David Ben-Gurion "waved his hand in a gesture which said, 'Drive them out.'" Tom Segev, discussing Plan Dalet, wrote that Yigael Yadin clarified Ben-Gurion's instructions to "break the spirit" of the Arab population, adding an appendix to the plan that gave the commanders the options of expelling the Arabs, cutting off essential services, including water and electricity, and "sowing terror" through propaganda.

Denialism