Why humanity’s appetite for war will never be sated

It’s easy to think that we’re living through a period of increasing warfare around the world. Ukraine and Russia, Israel and Gaza, the sabre-rattling of North Korea, Iran and even China; conflict in Yemen, in too many African states, anarchy in Haiti. So it goes on, yet really it has been ever thus. As Richard Overy points out, there wasn’t a single year in the 20th century in which there wasn’t a war going on, and there is evidence of violence and warlike behaviour since the emergence of Homo sapiens. But why does this occur? It’s a simple enough question and one that has led him to write a richly absorbing book as he delves into his quest for answers.

As he admits, he is a historian, and one of modern conflict, not a scientist, yet he is a man of ample intellect and well able to make a sideways slip into science here. And it is science to which he turns first, looking at biology, psychology, anthropology and ecology in turn to investigate whether these disciplines help provide answers as to why humankind – and especially men – have always felt compelled to go to war. “Nature keeps her human orchard healthy by pruning,” noted the biologist Sir Arthur Keith in 1931, “war is her pruning book”.

Yet Overy finds few answers in biology nor Freudian psychoanalysis, although psychology is different matter. After all, psychological factors have to come in to play to ensure the “in group” can sufficiently dehumanise the “out group” to persuade themselves to commit unspeakable violence against others without feeling any sense of moral guilt – and often even a sense of virtue, whether it be Hutus against Tutsis, French Catholics against Protestant Hugenots, or, of course, the Nazi state against Jews and Slavs. Ecology, too, has played its part, through climate change, droughts, or especially harsh winters. These are moments when acquiring food – and thus survival – has been challenging without taking it from others. In one of the wondrous nuggets of information that are sprinkled through this book, Overy tells us that in 1,000 years of Chinese history, for example, the 453 cold phases produced a total of 603 wars but that the 459 years of warmer climate led to only 296 wars, and that climate change arguably led to the collapse of three of China’s major dynasties. At the end of the last ice age, the global population was just 4.6 million; now it is nearly 8 billion.

A brief word of warning: the Biology chapter is a little hard work at times, which is unfortunate as it’s the first in the book. Do not be put off, however, as Overy’s narrative and arguments rapidly gather pace thereafter. The book really hits its straps once he gets into the chapters on Resources, Power, Security, and especially Belief, arguably the most compelling in the book. There are brilliantly recounted yet pithy summaries of the Crusades, the French Wars of Religion and even the emergence of the modern jihadists, Al Qaida and ISIS. The range of his studies is remarkable, especially for a shortish book: ancient Sintashta to Carthage and Rome, the Aztecs and Native American tribes, Nazi Germany and Putin’s Russia. It is also a history of the study of war – all the way from Scipio, Pope Urban II and Thomas Hobbes right through to modern thinkers.

The novelist LP Hartley famously claimed the past was a foreign country, but reading this fascinating book it’s hard not to be struck by the long threads of history and a sense of continuum. The differences between the motives for the First Crusade, Hitler’s war of conquest and the aims of ISIS are, for example, in terms of a powerful belief underpinning those conflicts, paper thin. History does not repeat itself but patterns of human behaviour clearly do, whether it be individual greed for power – Alexander the Great, Napoleon, Hitler, Putin – or whether it be outside factors threatening the security of certain peoples, or differences in culture that persuade one group that it is acceptable to destroy another. As Overy convincingly argues, there are lessons here that stretch all the way back into deep history. These patterns can help us look to the future too.

Richard Overy is unquestionably one of our finest living historians, especially of 20th-century warfare. For some reason, he is perhaps not as lauded as he should be despite seminal works such as The Road to War and his superb The Bombing War. He concludes, perhaps predictably, that there are many reasons why humankind has gone to war and will undoubtedly continue to do so; yet there is wisdom a-plenty in this small tome, and much to set the mind whirring. “If war has a very long history,” he ends prophetically, “it also has a future.” Let’s hope those of us who crave lasting peace can be ready for what may lie around the corner.

James Holland’s latest book is The Savage Storm: The Brutal Battle for Italy 1943. Why War? is published by Pelican at £22. To order your copy for £18.99 call 0808 196 6794 or visit Telegraph Books