The First World War was a watershed in the history of the Middle East, but its transformations reshaped not merely political boundaries, but also the collective imaginary of the Syro-Lebanese diaspora, or mahjar. In Cairo, Paris, New York, Buenos Aires and São Paulo, the major cities of the mahjar, emigrants from all sects of littoral Syria asserted new national understandings of Syria and Mount Lebanon in order to advance their careers and promote their preferred political order. While clerics and poets first articulated new ideas of Ottoman, Arab, Syrian, and Lebanese identity in nineteenth century, economic and intellectual elites from Beirut and Mount Lebanon advanced them anew in the uncertainty of war. Since then, political nationalists have inscribed teleologically ethnicity, race and nationality onto earlier history. However, this paper argues that diaspora activists fiercely contested the definitions, applicability and scope of identity politics in this dynamic period of change, as individuals and state institutions politicized belonging. In the mahjar, both in the Mediterranean and the Americas, immigrant journalists and activists remembered and redefined their homeland. The farther from Ottoman authorities and less involved in Ottoman governance, the easier it became for emigrants to imagine a post-Ottoman future. In newspapers, dramas, and political treatises, writers articulated a novel sacred-national understanding of Mount Lebanon and its place in the world. Even within families, there were divergences. The Druze notable Arslan family sent children to both the Ottoman civil service and separatist organizations; Amin, Muhammad, and Shakib Arslan deftly moved between Ottomanist, reformist, Lebanist, and Arab Nationalist camps. The Maronite Bustani and Sursock families similarly boasted both bureaucrats and dissidents. Sect was hardly the determining factor in ideology, as younger members of notable families had less incentive to preserve the Ottoman status quo. Nevertheless, the preponderance of Maronite and Orthodox Christians resident outside of the empire meant the missionary-educated Christian population formed an outsized role in dissident activist publishing in the areas beyond the reach of Ottoman press censorship. The predominantly Catholic milieu of France and Latin America and the relationship of mahjar intellectuals with conservative socio-political movements encouraged a Christian expression of Lebanese nationalism, embodied in the Classical-Biblical idea of Lebanon. Simultaneously, Islam and its relationship to the Arab homeland became an ideological battleground in the mahjar; the victory of the Allied Powers meant a victory for Lebanism and the nation-state order and a defeat for Ottomanism and Islamic Pan-Arabism.