Constantinople. In 1870 the Germans crossed the French frontier with 372,000 men, but after only a six weeks' campaign brought but 171,000 men to Paris. And so on. The result of it all is simple--that a people which is not based on the modern principle of the nation-in-arms cannot for long rival or contend with one that is, for it can neither put an equal (still less a superior) army into the field at the outset (_vide_ Clausewitz's first principle), nor even maintain in the field the _inferior_ army it does place there, because it cannot send the ever-required fresh supplies of trained troops. Sooner or later this must tell. Sooner or later a situation must arise in which the nation based on the obsolete voluntary system _must_ go down before a nation based on the nation-in-arms principle. Circumstances change with time, and, as wise Lord Bacon said long ago, "He that will not adopt new remedies must expect new evils." May we adopt the remedy before we experience the evil! THE MORAL AND SPIRITUAL FORCES IN WAR But though these changed conditions must, of course, _modify_ Clausewitz's details in many important particulars, still (to complete our circle and leave off where we started) I repeat that, as human nature never changes, and as the moral is to the physical as three to one in war, Clausewitz, as the great realistic and practical philosopher on the actual nature of war, as _the chief exponent of the moral and spiritual forces in war_, will ever remain invaluable in the study of war. Consider what unsurpassed opportunities he had for observing and reflecting on the influence of enthusiasm and passion, of resolution and boldness, of vacillation and weakness, of coolness and caution, of endurance and hardship, of patriotism and freedom, of ambition and of glory--on war, either by his own experience or by conversation with other equally experienced soldiers, during that long period of almost endless wars between 1793 and 1815.