This chapter shows the persistence of the imperial imagination in Baeck’s thought during the First World War, and his later critique of theological colonization during the Weimar Republic. When the Great War broke out, Baeck volunteered to serve as an army chaplain (Feldrabbiner), a position he held for almost the entire war period. Baeck’s sermons and writing from the front exemplify his view of the East as a space for colonization as well as his reading of the German military predicament as paralleling Jewish history. Baeck’s stature as a public intellectual rose during the Weimar Republic, but he also recognized a growing danger in the resurgence of the figure of second-century heretic Marcion, among others in the work of Adolf von Harnack, who called for a de-canonization of the Hebrew Bible. Baeck identified this tendency as central in the German theological and political imagination of the time. Against neo-Marcionite attempts to detach Christianity and Germany from Judaism and the Jews, Baeck offered a presentation of Judaism that stressed its place as the ethical foundation of Christianity. Only Judaism, Baeck insisted, could save Christianity from itself.