The law of nature, with respect to nations, is the same that it is with respect to individuals: it gives to the collective body a right to preserve themselves; to employ undisturbed the means of life; to retain the fruits of labour; to demand the observance of stipulations and contracts. In the case of violence, it condemns the aggressor, and establishes, on the part of the injured, the right of defence, and a claim to retribution. Its applications, however, admit of disputes, and give rise to variety in the apprehension, as well as the practice of mankind.

Nations have agreed universally, in distinguishing right from wrong; in exacting the reparation of injuries by consent or by force. They have always reposed, in a certain degree, on the faith of treaties; but have acted as if force were the ultimate arbiter in all their disputes, and the power to defend themselves, the surest pledge of their safety. Guided by these common apprehensions, they have differed from one another, not merely in points of form, but in points of the greatest importance, respecting the usage of war, the effects of captivity, and the rights of conquest and victory.

When a number of independent communities have been frequently involved in wars, and have had their stated alliances and oppositions, they adopt customs which they make the foundation of rules, or of laws, to be observed, or alleged, in all their mutual transactions. Even in war itself, they would follow a system, and plead for the observance of forms in their very operations for mutual destruction.

The ancient states of Greece and Italy derived their manners in war from the nature of their republican government; those of modern Europe, from the influence of monarchy, which, by its prevalence in this part of the world, has a great effect on nations, even where it is not the form established. Upon the maxims of this government, we apprehend a distinction between the state and its members, as that between the king and the people, which renders war an operation of policy, not of popular animosity. While we strike at the public interest, we would spare the private; and we carry a respect and consideration for individuals, which often stops the issues of blood in the ardour of victory, and procures to the prisoner of war a hospitable reception in the very city which he came to destroy. These practices are so well established, that scarcely any provocation on the part of an enemy, or any exigence of service, can excuse a trespass on the supposed rules of humanity, or save the leader who commits it from becoming an object of detestation and horror.