Strategy is the art of moving an army to advantage, so that either when it comes to fight it may do so on favourable terms, or it may gain ground on the enemy without fighting. An invasion so directed as to give the invader the command of the resources of a rich district, or to deprive the enemy of access to an important harbour, is an instance of the latter form of strategic movement. The former and commoner form, so moving as to compel the enemy to fight at some disadvantage, may take either of two shapes, or may involve both. There are two elements to be considered in comparing the situation of the combatants before a decisive battle. Which side has the best chance of winning? This depends mainly on the relative strength that can be brought into the field. To which side will the consequences of defeat be most serious? This depends mainly on the position of the two armies in the theatre of war. James IV. of Scotland, when the battle of Flodden was fought, had allowed Surrey to get between him and Scotland: here a defeat meant destruction. Henry V. was in a similar strait before Agincourt, but in this case victory in the field extricated him from danger. Obviously one of two combatants may begin with very inferior strength to his opponent; in that case he will probably be obliged to stand on the defensive, and his strategy must be directed to making the most of his force, to doing the best he can with very small numbers for minor purposes, to avoiding battle until he can equalise matters somewhat, and bring as large a proportion as possible to bear on the decisive point. Obviously also one side may have an advantage over the other derived from geography; for instance, one may have, while the other has not, a great fortress near the common frontier, which will serve as a starting point for invasion. A general has to take the facts as he finds them, and make the best of them. He is the most skilful strategist who gains the most without fighting, and who succeeds in shifting the balance most largely in his own favour before engaging in decisive battle.
Changes in tactics again are matters of great interest from age to age, not merely in themselves, but in connection with other developments on which at first sight they seem to have no bearing. Primarily they are matters of intellectual progress: the invention of gunpowder was an event of incalculable importance in human history. Similarly the material progress exemplified in making good roads brought with it the possibility of supplying an army in the field, instead of its being compelled to subsist on the country; and the possibility of doing this presently became a virtual necessity, because the best supplied army had a visible advantage. Thus gradually, through the progress of civilisation, armies have become highly elaborate machines, which require to be continuously supplied with food, ammunition, clothing, all the material without which they cannot act effectually. Hence they need to keep up continuous communication with their base of operations: and the conditions of strategy have been proportionally altered and rendered more complicated.
There are other changes in tactics, that is to say in equipment and mode of fighting, which may be called political: and it is not always easy to see whether they are the causes, or the effects, of social and political changes; possibly they are both. In the early middle ages, the feudal aristocracy was dominant politically, the mailed knights were preponderant on the battle-field. When infantry had learned on the continent of Europe to repel mailed cavalry with the pike, in England to destroy them with the clothyard arrow, the political supremacy of the feudal nobles waned along with their military superiority: their overthrow was consummated when the development of artillery placed feudal castles at the mercy of the crown. Inasmuch as political power must in the last resort depend on physical force, it is plain that the nature of the armed strength of a nation at any time will be an important element in determining the nature of its government.
There are also lessons to be learnt from battles which may roughly be called moral. Frederick the Great remarked cynically that, so far as he had observed, Providence was always on the side of the strongest battalions: and if the phrase be given sufficient width of interpretation it is perfectly true. No man ever exhibited more clearly than Frederick that strength has many elements. Discipline, endurance, mobility, courage, are all important constituents of military strength, as also is the relative excellence of armament. Soldiers who can be trusted not to lose their heads, either from eagerness or from panic, are worth far more in the long run than more excitable men. The bulldog, that never relaxes his grip but in death, is a more formidable opponent, weight for weight, than the tiger. Still more valuable is the iron tenacity which is capable of fighting after all hope is lost: it may apparently succumb, but such defeat is worth many a victory. The Spartans at Thermopylae were cut to pieces, but they taught the Persian king what Greeks could do, and prepared the way for his headlong flight when his fleet was beaten at Salamis: and the English in the Indian Mutiny enforced the same lesson. The individuals are lost to their country, but their death is worth more than many lives.
English history is in many ways well suited for illustrating the lessons that may be learnt from battles and their setting. It is continuous beyond any other national history of even moderate length. Englishmen of to-day have more in common with the axemen of Harold than Frenchmen of to-day have with the horsemen of Condé. Hence it is easier in England than elsewhere to see the significance of the changes, social and political, which accompany the military changes. The Norman feudal cavalry overcome the Saxon foot-soldiers, and the long-bow presently discomfits the lance; artillery makes mediæval walls worthless: the musket and pike supersede the bow, and the invention of the bayonet combines pike and musket in one. Later still have come enormous extension of the range of fire, both for infantry and artillery, the invention of new explosives and other engines of destruction, the effects of which are still matters of conjecture. Happily more than a generation has passed since British troops fought on a European battle-field: we have not yet tried long range artillery and machine guns, and cordite and melinite, and the other deadly things that end in -ite, except on a very small scale and against inferior races. But all the previous stages are reflected in our history of a thousand years, to go no further back than Alfred, and in some instances with very special significance.
Moreover English history is on the whole a history of success. We have suffered defeat from time to time, but the last crushing rout of a considerable army even mainly English, which history records, occurred nearly six centuries ago at the hands of our kindred the Scots, who have long since become our fellow-citizens. Why this has been the case is obvious enough; and the battle-fields point the moral very distinctly. First of all the English obtained a coherence of organisation and of feeling which entitled them to be called a nation, as that word is understood now-a-days, centuries before any other peoples of modern Europe; and the military value of that advantage is the foremost lesson of the so-called Hundred Years' War with France. Secondly, "the English don't know when they are beaten," as a great enemy said, in scorn for the stupidity of men who would fight on without perceiving that their opponents had gained tactical advantages, which to the quicker apprehension of some troops would have meant defeat. Such stupidity however is very difficult to distinguish from the dogged resolution which will not give way while life remains: and the quality, by whichever name it is called, is very apt to win. It needs no words to show that the lessons deducible from battles are more obvious to the victors; the losers have a great temptation to see only what may serve to excuse or palliate their defeat.
It may be added that in English history there is a considerable proportion of civil war, where the purely military aspect of things is not obscured by the possible or probable results of diversity of race. The conquest of India is also unique in history, for the mode in which it was achieved as well as for its extent. Thus English history gives every variety—its long continuity spreads its great battles over eight centuries, and those battles have been fought against European equals, in internal conflict, against the alien races of India. The only experience which England has not had is that of one armed nation precipitating itself on another; from this we are happily preserved by the narrow seas.