It is not the present intention to enter into any discussion of these different kinds of war, but rather to consider the general subject, and to discuss such general principles and rules as may be applicable to all wars. War in its most extensive sense may be regarded both as a _science_ and an _art_. It is a science so far as it investigates general principles and institutes an analysis of military operations; and an art when considered with reference to the practical rules for conducting campaigns, sieges, battles, &c. So is engineering a science so far as it investigates the general principles of fortification, and also artillery, in analyzing the principles of gunnery; but both are arts when considered with reference to the practical rules for the construction, attack, and defence of forts, or for the use of cannon. This distinction has not always been observed by writers on this subject, and some have asserted that strategy is the _science_, and tactics the _art_ of war. This is evidently mistaking the general distinction between science, which investigates principles, and art, which forms practical rules. In popular language, however, it is usual to speak of _the military art_ when we refer to the general subject of war, and of _the military sciences_ when we wish to call attention more particularly to the scientific principles upon which the art is founded. We shall here consider the military art in this general sense, as including the entire subject of war. As thus defined, the military art may be divided into four distinct branches, viz.: 1st. _Strategy_; 2d. Fortification, or _Engineering_; 3d. _Logistics_; 4th. _Tactics_. Several general treatises on this art add another branch, called _The Policy of War_, or the relations of war with the affairs of state. _Strategy_ is defined to be the art of directing masses on decisive points, or the hostile movements of armies beyond the range of each other's cannon. _Engineering_ embraces all dispositions made to enable troops to resist a superior force the longest time possible; and also the means resorted to by the opposing army to overcome these material obstacles. _Logistics_ embraces the practical details of moving and supplying armies. _Tactics_ is the art of bringing troops into action, or of moving them in the presence of an enemy, that is, within his view, and within the reach of his artillery. All these are most intimately connected. A fault in tactics may occasion the loss of strategic lines; the best combined manoeuvres on the field of battle may lead to no decisive results, when the position, or the direction of the operation is not strategic; sometimes not only battles, but entire campaigns, are lost through neglect of the engineer's art, or faults in his dispositions; again, armies would be of little use without the requisite means of locomotion and of subsistence.