Last weekend was the seventieth anniversary of the atomic bombing of Nagasaki, marked, as in Hiroshima a few days before, by solemn ceremonies of remembrance and sorrow. It is 70 years, therefore, since the world began to conduct its affairs under the shadow of the towering mushroom cloud that symbolises the awesome power of a nuclear bomb. Yet Nagasaki was the last attack of its kind, and new examples of nuclear horror have been held at bay. The reason is the strategic doctrine of “mutual assured destruction” – shortened to MAD – by which each side implicitly promises that any attack will be met by a counter-attack, inflicting unimaginable devastation. It was questionable morally, implying a conditional intention to commit the ultimate war crime, but it appeared t