This chapter examines the influences that Oswald Spengler's opus The Decline of the West had on contemporary philosophy. It describes affinities and similarities between that work and the historical critiques of reason prosecuted by Horkheimer and Adorno in their Dialectic of Enlightenment, and Heidegger's "history of Being'. At question is no less than the meaning of rationality, the place and purpose of truth, and the destiny of civilization. The discussion here limits itself to noting commonalities and similitudes, in the context of the wars.