There are several remarks to be made on conquest, considered as a method of acquiring the sovereignty. Conquest in itself is rather the occasion of acquiring the sovereignty, than the immediate cause of this acquisition. The immediate cause is the consent of the people, either tacit or expressed. Without this consent the state of war always subsists between two enemies, and one is not obliged to obey the other. All that can be said is, that the consent of the vanquished is extorted by the superiority of the conqueror.
Lawful conquest supposes, that the conqueror has had just reason to wage war against the vanquished.
Thus when Alexander waged war against distant nations, who had never heard of his fame, certainly such a conquest was no more a lawful tide to the sovereignty over those people, than robbery is a lawful manner of becoming rich. The quality and number of the persons do not change the nature of the action, the injury is the same, and the crime equal. Besides, the vanquished having, through their own fault, engaged in an unjust war, rather than grant the satisfaction they owed, are supposed to have tacitly consented to the conditions, which the conqueror should impose upon them, provided they were neither unjust nor inhuman. I answer, we should distinguish whether the usurper has changed the government from a republic into a monarchy, or dispossessed the lawful monarch. The law of nations therefore admits of a kind of prescription with respect to sovereignty.