The chapter analyses Zionist reactions to the outbreak of the First World War throughout the region. The war challenged traditional strategies and represented a severe crisis, both for the international Zionist movement, which fell apart and took new shape, and for local branches, drained of many of their members who were now in uniform. Zionists had vastly differing expectations of the war, which changed as the front moved eastwards and the Central Powers conquered much of Poland and the Baltic. As part of this German conquest of the East, several German Zionist activists travelled the region and tried to establish themselves as a leading force amongst East European Jewry. Their perception and representation of East European Jewry related to the type of nation-building they wanted to implement there. This project, which was fundamentally a ‘civilizing mission’, played out differently in the varying German occupation regimes of the Generalgouvernement Warschau and Ober Ost, and had profound impacts on local communities and activists, as well as on subsequent events. The chapter details the specific impact of the war on East-Central European Jewish societies, analysing the different occupation regimes and their diverse policies towards the Jewish population. It also demonstrates how Zionist concepts of nation, civilization, and modernity were adapted to local conditions and the immediate struggle for survival.