Voltaire described Europe as “a kind of great republic, divided into several states, some monarchical, the others mixed but all corresponding with one another. They all have the same religious foundation, even if it is divided into several confessions. They all have the same principles of public law and politics unknown in other parts of the world”. In a way that Charlemagne, Voltaire, William Penn and Gladstone, the early advocates of European unity, could only dream, a united Europe has become a reality with half a billion members. War, time and time again, has interrupted the pursuit of that objective. Continued civil war across the continent, across the centuries, has pitted the French against Germans, British against French, Czechs against Poles, Spaniards against Spaniards, Gentiles against Jews, reaching its dreadful climax in the Second World War. Of all the continents, over the millennium, Europe has been the most warlike. As...