The forty years from 1830 to 1870 saw a greater change in the means of warfare, both on land and sea, than during the whole previous span of modern history—or of all previous history. Most of the change was concentrated, at least in the sense of being demonstrated, within the last decade of the period. The technical, tactical, and strategical developments during the wars of this decade foreshadowed the operational trend, and social form, of warfare in the next century. Some of the new trends also exemplified the remarkable influence of two great military thinkers of the nineteenth century, Jomini and Clausewitz, whose main works appeared in the ’thirties.

For many centuries the strength of armies was reckoned in number of men, with merely a distinction between cavalrymen and infantrymen— ‘horse’ and ‘foot’, as the two branches, or arms, were customarily described. Subject to that distinction, of respective mobility, it was the most suitable way of computing their material strength before the advent of firearms, and it remained a reasonable form of reckoning so long as firearms were effective only at very short range, while still so inaccurate and slow-loading that the opponent had a good chance, especially if mounted, of coming to close quarters without being shot down. Even so, the volley-fire of infantry armed with the flint-lock musket became sufficiently effective with good training to put a strong curb on cavalry charges, and in the Napoleonic wars the cavalry arm was palpably a diminishing force. At the same time, field artillery played an increasingly important part in Napoleon's later battles, through improved tactical employment in concentrated numbers, so that it became more necessary in a reckoning of strength to count ‘guns’ as well as ‘horse and foot’.