In the eighth book of his classic On War Clausewitz describes what he understood to be the revolution in warfare which had taken place in his own lifetime. The wars of the eighteenth century, he says, were wars of kings not of peoples. National existence was not at stake (as certainly it was for Prussia after Austerlitz and Jena) but simply the conquest of an enemy province or two. Wars of this kind were affairs of the State, an autocratic State, and entirely separated from the interests of the people. Violence was restricted by calculation. In fact, this was what the twentieth century has come to call ‘limited war’.

After 1789, however, there was a profound change. Clausewitz goes on: “Whilst, according to the usual way of seeing things, all hopes were placed on a very limited military force in 1793, such a force as no one had any conception of made its appearance. War had again suddenly become an affair of the people, and that of a people numbering thirty millions, every one of whom regarded himself as a citizen of the State….

After all this was perfected by the hand of Buonaparte, this military power, based on the strength of the whole nation, marched over Europe, smashing everything in pieces so surely and certainly, that where it only encountered the old-fashioned Armies the result was not doubtful for a moment. A reaction, however, awoke in due time. [Elsewhere] the War became of itself an affair of the people….