War between states has been accepted as the only legitimate form of violence as long as states have existed. In pre-1914 Europe recourse to war was recognized by statesmen as a normal and acceptable instrument of policy and diplomacy – an extension of politics by other means, in the famous formulation of Clausewitz. In the twentieth century, however, the character of war was transformed. Wars were waged with unprecedented savagery: the rules of war formulated over centuries and codified in The Hague Conventions of 1899 and 1907 were ignored as states abandoned the notion of limited war in favour of all-out, ‘total’ or ‘apocalyptic’ war, pursued for ideological ends. Herbert Butterfield, Regius Professor of Modern History at Cambridge University, characterized each of the two world wars as ‘a war for righteousness’, which he defined as a war ‘in which the conflict of right and wrong admitted of no relenting’. In this regard, Butterfield contended, the total wars of the twentieth century recalled the wars of religion of the sixteenth and seventeenth centuries which statesmen and political thinkers since the Enlightenment had viewed with horror as an affront to civilization. The deadliest features of twentieth-century warfare, according to Butterfield, were the product not of modern technology but of a theory of war which eschewed all restraint or limits. Hatred, viciousness, a refusal to compromise – these were the characteristics of the modern ‘war for righteousness’, conferring on conflict what Butterfield called a ‘daemonic’ quality.