This study engages in the period of inter-communal war in Palestine, from December 1947 to May 1948. The belligerents in this conflict were the Yishuv (pre-state Jewish community in Palestine) on one side, and the Palestinian Arabs, aided by some volunteers from Arab countries, on the other side. During this war, the larger 'mixed' cities, Jerusalem, Jaffa and Haifa, became a main battlefield. The Palestinian Arab communities in Jerusalem and Jaffa were chosen as a case study for their size, centrality, and significance to the Palestinian Arab community and national movement. A well-known Palestinian Historian called for research to uncover the internal reasons for the Palestinian debacle in 1948, alongside the well-known external reasons, particularly the Yishuv's military superiority. This study, in response, engages in the Palestinian local arena by using a comparative approach, in order to find better explanations for this military and social collapse. The main hypothesis is that social and geopolitical characteristics, accruing especially to Jaffa, led to the rapid and total collapse of this city vis-y-vis Jerusalem. On a countrywide scale, those traits brought about the disintegration and collapse of the Palestinian Arab Society under Jewish military pressure. The findings show differences in patterns of political, social and economic organization, stemming out of different characteristics of the population and the social changes undergone during the Mandate era. This study describes, in addition, how the rise of a middle class under the Mandate, mainly in the larger cities, accelerated the fall of the Palestinian Arab society in 1948, since members of this class tended to abstain from taking part in the national struggle and the war effort. The research is based on: Arab documents; Palestinian and Arab press of the time; diaries, memoirs and testimonies; and intelligence archival material (Israeli and British). Most researches on the 1948 War period had focused, so far, on the political and military aspects. This study contributes to the study of the Palestinian Arabs in 1948 from the social point of view, which was mainly neglected by research so far