On Friday 10 May 1940, a little after 6pm, Winston Churchill walked out of Buckingham Palace, where King George VI had just asked him to become prime minister and form a government. Now, at last, at the age of sixty-five and almost forty years since he had first become an MP, Churchill had achieved a life’s ambition. He went to bed in the early hours of the next morning with, as he put it in his memoirs, ‘a profound sense of relief. At last I had the authority to give directions over the whole scene. I felt as if I were walking with destiny, and that all my past life had been but a preparation for this hour and for this trial.’ Some trial: only that morning Hitler had unleashed his panzers on the Low Countries and France. The violence, terror and horror that began that day would end only five years later, in the smoking ruins of Hiroshima and Berlin.

Part of the reason why Churchill thought he was ‘walking with destiny’ was his previous experience of war, both on the frontiers of the Victorian empire and as a government minister and an infantry officer on the Western Front during the First World War. In The Strategists, Phillips Payson O’Brien examines how the battles Churchill and four of the other major leaders of the Second World War – Stalin, Hitler, Roosevelt and Mussolini – fought as young men affected the strategies they pursued between 1939 and 1945. The first half of the book serves up potted biographies of the men before 1939, while the second presents ten case studies of strategic decision-making during the war, from the Nazi–Soviet Pact that enabled Hitler to launch his attack on Poland to the D-day invasion.

These are five of the most famous and written-about men in history, but O’Brien is seeking to do something more useful than rehashing all the old stories. He is trying to set the Second World War in deeper historical context by drawing out connections with the First World War. Further,