In reading Clausewitz it is, first, the great principles of the nature of war founded on human nature, which alter not; and, secondly, it is his spirit and practical way of looking at things that we want to assimilate and apply to THE PROBLEMS OF TO-DAY, to which end it is necessary to read him always with the changed conditions of to-day in our minds, and think what he would have said under the circumstances. These changes are chiefly:​—​

The Improved Net-work of Roads

The improved net-work of roads in Europe (not, of course, in Manchuria, or in Afghanistan where we have to consider our future strategy, but in Europe), as General v. Caemmerer puts it, "now offers to the movements of armies everywhere a whole series of useful roads where formerly one or two only were available," easier gradients, good bridges instead of unreliable ones, etc. So that the march-discipline of that day when concentrated for battle, artillery and train on the roads, infantry and cavalry by the side of the roads, has disappeared. Such close concentration is therefore now not possible, as we move all arms on the road, and an army corps with train, or two without, is the most that we can now calculate on bringing into action in one day on one road.

Railways

"Railways have, above all, completely altered the term 'base,'" remarks V. Caemmerer. "Railways carry in a few days men, horses, vehicles, and materials of all kinds from the remotest district to any desired point of our country, and nobody would any longer think of accumulating enormous supplies of all kinds at certain fortified points on his own frontier with the object of basing himself on those points. One does not base one's self any longer on a distinct district which is specially prepared for that object, but upon the whole country, which has become one single magazine, with separate store-rooms. So the term 'base' has now to be considered in this light."

It is only when operating in savage or semi-savage countries, where there are no railways, that the old idea of a base applies.

As we penetrate deeper and further from our own country into the enemy's, and as a small raiding party can demolish the railway line so as to stop all traffic for days or weeks, it becomes far more necessary than it ever was in Clausewitz's day to guard our communications. And armies become more and more sensitive to any attack upon their communications.

Also "such a line cannot easily be changed, and consequently those celebrated changes of the line of communication in an enemy's country which Napoleon himself, on some occasion, declared to be the ablest manœuvre in the art of war, could scarcely be carried out any more" (V. Caemmerer).

Also concentration by means of several railways demands a broad strategic front, which produces that separation of corps or armies which prepares the way for strategical envelopment, and so on.