 These facts about the twentieth century raise problems for the philosophy of history for several reasons. They challenge historians to consider the depth, detail, and human experience that the historian must convey of the events and experiences that war, genocide, and totalitarianism imposed on millions of people. The discovery and truthful documentation of the extent and lived experience of these crimes is a painful but crucial necessity. Second, historians are forced to reflect on the assumptions they bring to their research and interpretations – assumptions about geography, political causation, individual motivation, and behavior resulting in these crimes. Third, historians must reconsider and sharpen their hypotheses about causation of these vast and extended crimes against humanity. Fourth, it appears inescapable that historians have a human responsibility to contribute to worldwide changes in culture, memory, and politics in ways that make genocide and totalitarian oppression less likely in the future.