The time since the Second World War has been seen by some as the longest uninterrupted period of harmony in human history: the ‘long peace’, as Stephen Pinker called it. But despite this, there has been a military conflict ongoing every year since 1945. The same can be said for every century of recorded history. Is war, therefore, an essential part of being human? In ‘War’, Professor Margaret MacMillan explores the deep links between society and war and the questions they raise. We learn when war began – whether among early homo sapiens or later, as we began to organise ourselves into tribes and settle in communities. We see the ways in which war reflects changing societies and how war has brought change – for better and worse. Economies, science, technology, medicine, culture: all are instrumental in war and have been shaped by it.