But it is clear that this supposed right to kill the conquered is by no means deducible from the state of war. Men, from the mere fact that, while they are living in their primitive independence, they have no mutual relations stable enough to constitute either the state of peace or the state of war, cannot be naturally enemies. War is constituted by a relation between things, and not between persons; and, as the state of war cannot arise out of simple personal relations, but only out of real relations, private war, or war of man with man, can exist neither in the state of nature, where there is no constant property, nor in the social state, where everything is under the authority of the laws.
Individual combats, duels and encounters, are acts which cannot constitute a state; while the private wars, authorised by the Establishments of Louis IX , King of France, and suspended by the Peace of God, are abuses of feudalism, in itself an absurd system if ever there was one, and contrary to the principles of natural right and to all good polity.
War then is a relation, not between man and man, but between State and State, and individuals are enemies only accidentally, not as men, nor even as citizens, but as soldiers; not as members of their country, but as its defenders. Finally, each State can have for enemies only other States, and not men; for between things disparate in nature there can be no real relation.
Furthermore, this principle is in conformity with the established rules of all times and the constant practice of all civilised peoples. Declarations of war are intimations less to powers than to their subjects. The foreigner, whether king, individual, or people, who robs, kills or detains the subjects, without declaring war on the prince, is not an enemy, but a brigand. Even in real war, a just prince, while laying hands, in the enemy’s country, on all that belongs to the public, respects the lives and goods of individuals: he respects rights on which his own are founded.