"But in the wars of the French revolution, although the levee en masse decreed in France 16th August 1793 had no grounding in procedure, the forced requisitions, in augmenting immensely the number of combatants, torn from the national industries to act offensively against the enemies, at last forced the latter to imitate this new example of which the results will be incalculable for the peace and prosperity of the nations, if it becomes the pattern for future wars."
When you get the general populace involved, in Spain as in Naples, and later in Russia, you are then dealing with a large body of people who have not read the laws of war and who probably take the view that soldiers who invade their country, insult their religion, burn their houses and rape their women do not deserve any form of consideration. The consequence of this is that the soldiers start to consider all civilians, male and female, as potential assassins and to treat them accordingly.
It all goes downhill from there and no amount of study of the Laws of Nations will help.
regards,
Susan