In the fourth century BC, Thucydides summarised war as 'the human thing', the activity which defines humanity. In his work 'Why War' Christopher Coker is inclined to agree arguing that war encapsulates the full panorama of human experience and is a clear means of distinguishing homo sapiens from the rest of the animal kingdom. In our latest episode of History Lessons, he and Mattias consider humanity's most primitive proclivity for violence, from the earliest of human conflicts to whether a world without war is possible, or even desirable.