I’ll start with a mea culpa. For a long time, I have dismissed the West’s enemies as small fry, unambitious and far away. And, for a long time, I have advocated an anti-interventionist line in dealing with them. But the massacre of Christians in the Middle East and Russia’s transparent abuse of ceasefire agreements in Ukraine has made me fear that I might have mistaken cowardice for realism. Nicholas Wapshott’s The Sphinx tells the story of an unnervingly similar epoch, in which canny interventionism proved to be a wiser course.

The titular sphinx is Franklin D Roosevelt, so described because it was impossible to tell what he was thinking. That quality proved useful in the late 1930s and early 1940s when the president had to confront war in Europe and couldn’t afford to let the American voter know his real