Public theology that does not reckon closely with awkward social, economic and political realities cannot expect to command the respect of those burdened with making and implementing public policy. There is a tradition in Anglican ethics that has long understood this. Let us call it ‘Anglican Christian Realism’. Of course, talk of ‘Christian Realism’ immediately brings Reinhold Niebuhr to mind. However, long before Niebuhr, Anglican ethics had taken a realist turn. Insofar as it denotes an ethic that is willing to have its rules of conduct and moral judgements informed by a sober reckoning with human realities, especially political ones, Christian Realism can be found in Anglican England at least as far back as the late sixteenth century. For it was then that Alberico Gentili (1552-1608)—a Protestant refugee from Italy, who became Regius Professor of Civil Law at the University of Oxford and had close ties to the court of Queen Elizabeth I—published De Jure Belli Libri Tres (Three Books on the Laws of War, 1588-89, 1598). In this he presented a systematic account of the ethics of war, but one that, eschewing ‘the scholastic method, … [which] entailed virtually pure logical analysis with very little historical perspective’, was nourished by unusually close attention to historical examples, military practice, and actual events.¹ Acutely mindful of the political reality of English vulnerability to aggression from imperial Spain, Gentili developed ‘just war’ thinking in a controversially permissive direction, arguing in favour of ‘preventative’, as distinct from ‘pre-emptive’, war. The latter is a defensive action taken at the eleventh hour against an attack that is known to be in the process of being realised and that will be launched at midnight. The former is a ‘defensive’ action taken against a party that might, at some indeterminate time in the future, become an active threat, but is not presently. Accordingly, he wrote: