THE nature of the things does not allow of a completely satisfactory definition of these three factors, denoting respectively, space, mass, and time in war; but that we may not sometimes be quite misunderstood, we must try to make somewhat plainer the usual meaning of these terms, to which we shall in most cases adhere.
1.—Theatre of War.
This term denotes properly such a portion of the space over which war prevails as has its boundaries protected, and thus possesses a kind of independence. This protection may consist in fortresses, or important natural obstacles presented by the country, or even in its being separated by a considerable distance from the rest of the space embraced in the war.—Such a portion is not a mere piece of the whole, but a small whole complete in itself; and consequently it is more or less in such a condition that changes which take place at other points in the seat of war have only an indirect and no direct influence upon it. To give an adequate idea of this, we may suppose that on this portion an advance is made, whilst in another quarter a retreat is taking place, or that upon the one an army is acting defensively, whilst an offensive is being carried on upon the other. Such a clearly defined idea as this is not capable of universal application; it is here used merely to indicate the line of distinction.
With the assistance of the conception of a Theatre of War, it is very easy to say what an Army is: it is, in point of fact, the mass of troops in the same Theatre of War. But this plainly does not include all that is meant by the term in its common usage. Blucher and Wellington commanded each a separate army in 1815, although the two were in the same Theatre of War. The chief command is, therefore, another distinguishing sign for the conception of an Army. At the same time this sign is very nearly allied to the preceding, for where things are well organised, there should only exist one supreme command in a Theatre of War, and the commander-in-chief in a particular Theatre of War should always have a proportionate degree of independence.
The mere absolute numerical strength of a body of troops is less decisive on the subject than might at first appear. For where several Armies are acting under one command, and upon one and the same Theatre of War, they are called Armies, not by reason of their strength, but from the relations antecedent to the war (1813, the Silesian Army, the Army of the North, etc), and although we should divide a great mass of troops intended to remain in the same Theatre into corps, we should never divide them into Armies, at least, such a division would be contrary to what seems to be the meaning which is universally attached to the term. On the other hand, it would certainly be pedantry to apply the term Army to each band of irregular troops acting independently in a remote province: still we must not leave unnoticed that it surprises no one when the Army of the Vendeans in the Revolutionary War is spoken of, and yet it was not much stronger.
The conceptions of Army and Theatre of War therefore, as a rule, go together, and mutually include each other.
Although the sum of all military events which happen in all the Theatres of War in one year is often called a Campaign, still, however, it is more usual and more exact to understand by the term the events in one single Theatre of War. But it is worse still to connect the notion of a Campaign with the period of one year, for wars no longer divide themselves naturally into Campaigns of a year's duration by fixed and long periods in winter quarters. As, however, the events in a Theatre of War of themselves form certain great chapters—if, for instance, the direct effects of some more or less great catastrophe cease, and new combinations begin to develop themselves—therefore these natural subdivisions must be taken into consideration in order to allot to each year (Campaign) its complete share of events. No one would make the Campaign of 1812 terminate at Memel, where the armies were on the 1st January, and transfer the further retreat of the French until they recrossed the Elbe to the campaign of 1813, as that further retreat was plainly only a part of the whole retreat from Moscow.
That we cannot give these conceptions any greater degree of distinctness is of no consequence, because they cannot be used as philosophical definitions for the basis of any kind of propositions. They only serve to give a little more clearness and precision to the language we use.