Nations, that is to say, the agreements made between governments, should be brought into harmony with the principles of natural morality and the commands of justice written, as he said, by God on the hearts and minds of men. This he called the Law of Nature, which man could discover by right reason. He wanted, in fact, the same ideas of right and wrong which people were taught to adopt in their dealings with one another to be applied to the dealings of one nation with another. Instead of saying that justice, honor, generosity, and friendship meant one thing between man and man and quite another thing between nation and nation, he tried to combine the two and bring the lower one up to the level of the higher. Out of this union between the two sorts of law he hoped to create an international law which would put an end to the unreasonable, uncivilized, and perpetually dangerous relationship which existed between nations.
The great book he wrote was called "De Jure Belli ac Pacis" (Concerning the Law of War and Peace). He collected together in it quotations from a number of great men, and elaborated his argument with wonderful clearness and great learning. He condemned the atrocities of warfare, and more especially he pointed to a way in which war might be avoided. He examined various methods by which international questions might be settled without war, and proposed the idea of conferences and international arbitration.
