To teach infantry that they can thus withstand cavalry, instruction is the instrument. You must drill them, and form them constantly, and hammer it into them by repeated statement that if they stand firm all will be well. This has been done in the case of men on foot armed only with staves. It is easier, of course, to inculcate the lesson when they are possessed of missile weapons; for a continued discharge of these is impossible from charging riders, and an infantry force armed with missile weapons, and unshaken, can be easily persuaded by training, and still more by experience, that it can resist cavalry. Under modern conditions, where missile weapons are of long range and accurate, this goes without saying; but even with a range of from fifty to eighty yards of a missile that will bring down a horse or stop him, infantry can easily be made sufficiently confident if it is unshaken. Now, to shake it, there is nothing available (or was nothing before the art of flying was developed) save other men, equally stationary, armed with other missiles. The long-bowman of the Plantagenets knew that he had a missile weapon superior to anything that his enemy could bring against him. He therefore stood upon the defensive against a feudal cavalry charge unshaken, and he was trained by his experience and instruction to know that if he kept his line unbroken, the cavalry charge would never get home. That is the supreme tactical factor of the Plantagenet successes of the Hundred Years' War.
The immediate results of the victory of Poitiers consisted, first, in the immensely increased prestige which it gave to the House of Plantagenet throughout Europe.
Next, we must reckon the local, though ephemeral, effect upon the opinion of Aquitaine, through which the Black Prince was now free to retreat at his ease towards Bordeaux and the secure territories of Gascony.
But though these results were the most immediate, and though the victory of one monarch over the other was the most salient aspect of the victory for contemporaries, as it is for us, there was another element which we must particularly consider because it illustrates the difference between the political conditions of the fourteenth century and of our own time.