This article is about the problem of the unity of history as seen through the writings of Karl Löwith. By “unity of history” I understand the notion that all history constitutes one and only one range of kinds of objects and/or one field of knowledge. The article argues that the problem of the unity of history—though often neglected as a matter of mere argumentative infrastructure—is central to a number of wider problems, most prominently the possibility of a plural understanding of historicity and the possibility of ultimately avoiding a unified historical teleology. The article revisits Löwith's writings and proposes a variety of novel interpretations with the aim of evincing the centrality, and of exploring diverse aspects, of the problematic of the unity of history. This problematic is shown to have informed Löwith's work on the secularization thesis as well as his debate with Hans Blumenberg. The foundations of Löwith's discussion of the problem are pursued across his ambivalent critique and appropriation of Heidegger's model of an ontology of historicity as marked by inevitable internal conflict and thus disunity. The paper reconstructs the manner in which, after the Second World War, Löwith's philosophy of history sought to salvage basic traits of the Heideggerian model when it tried to establish the possibility of plural historicity from a notion of the natural cosmos. It is demonstrated that the motives for this salvage operation ultimately extended beyond the problem of Löwith's reception of Heidegger and concerned the possibility of continuing any debate on the philosophy of history.