This paper explores the question whether war was regarded as eugenic or dysgenic before, during and after the First World War. The main focus is on the positions of the German military officer and historian Friedrich von Bernhardi, who in Germany and the Next War, first published in 1912, argued for war as eugenic, and Vernon Kellogg’s Headquarters Nights, published in 1917, which marks an important work characterizing war as dysgenic. I argue that an international community of biologists and social (...) scientists who debated the hereditary effect of war existed before World War I and trace how the concepts of altruism and group selection contributed to a eugenic or dysgenic interpretation of war. (shrink)