Oh yes, Clausewitz: we shall all have to dust him off and read him again, for there is nobody else to make sense of the infernal logic that is now grinding back into action. The Prussian soldier with a philosophical bent—a late flower of the tradition that produced Frederick the Great and Immanuel Kant—pursues us remorselessly with his definition of war as “an act of force to compel our enemy to do our will . . . and there is no logical limit to the application of that force”. Clausewitz will have no truck with the notion that “civilised” nations must necessarily prosecute war less destructively than others. The French Revolution and the Napoleonic wars had changed everything: “Bonaparte’s audacity and luck have cast the old accepted practices to the winds. Major powers were shattered with virtually a single blow.” Not only the French, but the Spanish, Russians and Prussians had “shown what an enormous contribution the heart and temper of a nation can make to the sum total of its politics, war potential, and fighting strength. Now that governments have become conscious of these resources, we cannot expect them to remain unused in the future, whether the war is fought in self-defence or in order to satisfy intense ambition.”

The prophecy of On War in 1832 has proved all too accurate over the past two centuries. In 1915, a century ago, the introduction of poison gas by the Germans at the Second Battle of Ypres marked the advent of weapons of mass destruction— an early example of the alarming alliance of science and warfare. (The chemist responsible for developing the lethal use of gas on an industrial scale was Fritz Haber, who by a terrible irony was a German Jew.) In Syria and Iraq today, chemical weapons are still being deployed by the Assad regime and ISIS indiscriminately against soldiers and civilians. The Germans tried to persuade the world that Allied accusations of “atrocities” were mere propaganda, with considerable success; and indeed the Allies soon retaliated with chemical warfare too. Among the tens of thousands who were gassed was a corporal named Adolf Hitler. Within a generation he had demonstrated that mere atrocities were obsolete, now that the new concept of “genocide” was within the power of the modern state. The “total war” invoked by Goebbels in his notorious speech at the Sportpalast in 1943—“Do you want total war?” he screamed, and the crowds roared back their approval—exceeded anything that had been seen before, but this time the Germans themselves reaped the whirlwind. By 1945, for much of humanity war had become a way of life as well as death. Nothing and nobody was sacrosanct.

In a macabre re-enactment of this hellish past, the Communist world remained locked into perpetual belligerence. Memorials, parades, conscription, training preserved the Eastern bloc in a state of permanent mobilisation. If the West offered welfare from cradle to grave, Communism offered warfare from cradle to grave. It was all done in the name of peace, but the road to the Gulag was paved with pacific intentions. Today, that pattern is visible once again. The contrast between the remilitarisation of Russia and the demilitarisation of the West has become too obvious to ignore. For the free world, martial artlessness is a source of pride; not so for those who see us as the foe. Democracies may have no enemies among their own kind, but to make disarmament the touchstone of decency ignores the existence of others who do not play by our rules. Faced by the threat of international anarchy, with predators such as Putin’s Russia and the Islamic State preying on their neighbours, the West runs the risk of repeating the mistakes that made both world wars possible and came close to costing us the Cold War too. Foremost among these mistakes is the notion that Immanuel Kant’s dream of perpetual peace can be guaranteed by global institutions as such, rather than by the nation states that created those institutions.