An excerpt from, "Napoleon On War" Edited By Bruno Colson, Translated By Gregory Elliott, Oxford University Press, 2015, Pg. 298:
Arming the people in a war that had become a national war was alluded to in a conversation of January 1818. Gourgaud said that conquests could now no longer be made as they had been in the past, by destroying nations. Napoleon added:
Firearms are contrary to conquests, because a mere peasant with such a weapon is worth a brave man. Thus, in a national war where the whole population takes up arms there is an adventure in this new state of affairs.For Napoleon, the war in Spain proved nothing. But he said this to exculpate himself, blaming circumstances, his generals, and, above all, his brother Joseph. Moreover, the works of Charles Esdaile have clearly established that the role of the guerrillas was unduly glorified by politicians and publicists and that the regular army played the essential role alongside Wellington's forces. The Spanish and Portuguese guerrillas played a certain role, but were more like collections of brigands than a 'people in arms'.
However that may be, the tasks to be entrusted to the people in arms were not those of the regular army. Essentially, their role was to supply positions with garrisons:
The garrisons of strongholds must be drawn from the population and not from active armies. Regiments of the provincial militia used to serve this purpose: it is the most splendid prerogative of the national guard.For Clausewitz, 'a popular uprising should, in general, be considered as an outgrowth of the way in which the conventional barriers have been swept away in our lifetime by the elemental violence of war. It is, in fact, a broadening and intensification of the fermentation process known as war. According to Clausewitz, however, a war in which the people are involved must always be combined with the war conducted by the standing army, and conducted in accordance with a single overall plan. Popular levies must not be used against the enemy's main corps or even against any sizeable corps: 'They are not supposed to pulverize the core but to nibble at the shell and around the edges.' These ideas coincide with those of the Emperor.
