The thesis analyzes Zionism as a nation building project in East-Central Europe during the years of war, revolution, the collapse of Empires and the creation of nation states, 1914 to ca. 1920. It focuses on the day-to-day forms of activism in the Habsburg Empire and the regions of Russia occupied by the German army during the First World War. Zionist activists found themselves in a situation where they both had to respond to hitherto unknown pressures and where they could seize opportunities to engage with the masses of East-Central European Jewry and win them to the national project. The thesis argues that it was the everyday encounters between Zionist activists and Jewish communities that allowed the movement to establish itself as an important force in Jewish social and political life. These included the building of a social and educational infrastructure, the provision of relief and aid as well as attempts to provide security and representation during a period that was characterized by impoverishment and anti-Jewish violence. Local conditions and the relations between activists and the authorities determined whether such efforts were successful and whether Zionists could convince larger segments of the population and acquire meaningful positions within Jewish society. The Zionist activists’ struggle to gain agency for the Jewish nation in a radically changing environment is at the core of the thesis. The major narratives of the period, namely those of collapse of empires, the rise of nationalism, and the simultaneous promises made by the Balfour Declaration and the Russian Revolution could have different impacts and meanings on a local level and for individual activists. Whereas many of these developments forced people to rethink their ideological preconceptions as well as their place in society, I argue that Zionists’ on-the-ground activism shaped the way people responded to these major events.