Led by his previous studies to test every thing by the question of right, Proudhon asks, in his "War and Peace," whether there is a real right of which war is the vindication, and victory the demonstration. This right, which he roughly calls the right of the strongest or the right of force, and which is, after all, only the right of the most worthy to the preference in certain definite cases, exists, says Proudhon, independently of war. It cannot be legitimately vindicated except where necessity clearly demands the subordination of one will to another, and within the limits in which it exists; that is, without ever involving the enslavement of one by the other. Among nations, the right of the majority, which is only a corollary of the right of force, is as unacceptable as universal monarchy. Hence, until equilibrium is established and recognized between States or national forces, there must be war. War, says Proudhon, is not always necessary to determine which side is the strongest; and he has no trouble in proving this by examples drawn from the family, the workshop, and elsewhere. Passing then to the study of war, he proves that it by no means corresponds in practice to that which it ought to be according to his theory of the right of force. The systematic horrors of war naturally lead him to seek a cause for it other than the vindication of this right; and then only does the economist take it upon himself to denounce this cause to those who, like himself, want peace. The necessity of finding abroad a compensation for the misery resulting in every nation from the absence of economical equilibrium, is, according to Proudhon, the ever real, though ever concealed, cause of war. The pages devoted to this demonstration and to his theory of poverty, which he clearly distinguishes from misery and pauperism, shed entirely new light upon the philosophy of history. As for the author's conclusion, it is a very simple one. Since the treaty of Westphalia, and especially since the treaties of 1815, equilibrium has been the international law of Europe. It remains now, not to destroy it, but, while maintaining it, to labor peacefully, in every nation protected by it, for the equilibrium of economical forces. The last line of the book, evidently written to check imperial ambition, is: "Humanity wants no more war."