It is, I know, a rash proceeding to appraise the importance of any single factor in the complicated and shifting field of military history. And if I venture on this occasion to rush in where more competent historians would fear to tread, and hazard a few generalisations on the influence of certain tactical ideas, I do it, not in the expectation of making any contribution to your knowledge, but in the hope that, possibly, my rough and imperfectly based conclusions may suggest a useful line of inquiry. I ought, perhaps, to begin by making it clear that in using the expression “tactical idea” I am not referring so much to the idea of the commander in disposing his forces for action, as to something much more elementary, namely, the general idea or style of fighting in which the ordinary soldier is trained—the ultimate factor which underlies leadership in the field and in the campaign. Military history, like most other history, is usually surveyed from the top downwards. We study the political and economic motives and causes of a war, we follow the operations of strategy, we pore over the dispositions of the battlefield, and then, lastly, we note the fighting equipment and methods of the ordinary soldier. But it may not be amiss, for once in a way, to invert the order of importance, treat the soldier and his notion of fighting as the dominating element, and relegate the great generals and the fate of empires and civilisations to a secondary and consequential position.