What were the effects of the Great War on religious life of East European Jews, as exemplified by its most visible, Hasidic section? What was unique in Hasidic experience of the Great War? This essay discusses the human and material losses suffered by the Hasidic movement, changes in the movement’s geography, ideological and political transformations surrounding and within Hasidism, and—most importantly—the specific changes in Hasidism caused by these transformations. It agues that Hasidism after 1918 found itself in a radically new situation, and despite the fact that many of its institutions were, on the face of it, working more or less as they had done before the war, the movement experienced a profound transformation of its geography, social roles, institutional bonds, and, often, identification with Hasidism. In this regard, the First World War was a key accelerator of the processes which transformed the Hasidic movement during the interwar period, and eventually to a significant extend shaped its resurrection and renaissance after the Holocaust.