Darwinian evolutionary theory is one of the brightest jewels in the crown of science, yet it has been highly controversial since its first appearance in the On the Origin of Species in 1859. Well known is the opposition of so many Christians, an opposition that shows little sign of abating today. In The Problem of War, philosopher Michael Ruse argues that the roots of the unease lie not simply (as many think) in a straight clash between science and religion, but more deeply in the fact that, while professional biologists are producing first-class science, Darwinism has always had a somewhat darker side where it functions as a secular religion, a form of humanism, directly challenging Christianity. Testing and confirming this claim, The Problem of War is an in-depth study of Christians and of Darwinians on the theme of war. It covers a wide range of thinkers: on the Christian side from Augustine to modern theologians such as Reinhold Niebuhr and Karl Barth, to the present Regius Professor of Theology at Oxford Nigel Biggar; and on the Darwinian side from Darwin himself to more modern thinkers like Konrad Lorenz, Frans de Waal, and the present Johnstone Family Professor in the Department of Psychology at Harvard, Steven Pinker. Ruse shows that the dynamic between Darwinians and Christians has not been a straightforward opposition, and complicates as it moves through the 20th century, as some Christian thinkers start to favor the inevitability of war and Darwinians acknowledge the idea of moral progress. Ruse shows how in some cases, some were even able to integrate Darwinian and Christian perspectives on war. Best categorized as intellectual history, The Problem of War is a narrative, using a wide and deep breadth of knowledge and references to reveal nuances in how war as a core function of human nature has been understood. By appreciating the religious nature of the dispute, Ruse helps to foster a better understanding of the ongoing criticisms of Darwinism and creates a way for differing Christian and Darwinian perspectives to indeed find common meeting ground.