Grotius, I. c. 3; II. c. 1; III. c. 3--Pufendorf, VIII. c. 6, § 9--Vattel, III. §§ 2, 5, 24-50, 183-187--Lorimer, II. pp. 29-48--Phillimore, III. §§ 33-48--Twiss, II. §§ 26-30--Halleck, I. pp. 488-519--Taylor, §§ 452-454--Wheaton, §§ 295-296--Bluntschli, §§ 515-521--Heffter, § 113--Lueder in Holtzendorff, IV. pp. 221-236--Klüber, §§ 41, 235, 237--G. F. Martens, §§ 265-266--Ullmann, § 166--Bonfils, Nos. 1002-1005--Despagnet, No. 506--Pradier-Fodéré, VI. Nos. 2661-2670--Rivier, II. p. 219--Nys, III. pp. 106-114--Calvo, IV. §§ 1866-1896--Fichte, _Ueber den Begriff des wahrhaften Krieges_ (1815)--Rettich, _Zur Theorie und Geschichte des Rechts zum Kriege_ (1888), pp. 141-292--Peyronnard, _Des causes de la guerre_ (1901). [Sidenote: Rules of Warfare independent of Causes of War.] § 61. Whatever may be the cause of a war that has broken out, and whether or no the cause be a so-called just cause, the same rules of International Law are valid as to what must not be done, may be done, and must be done by the belligerents themselves in making war against each other, and as between the belligerents and neutral States. This being the case, the question as to the causes of war is of minor importance for the Law of Nations, although not for international ethics. The matter need not be discussed at all in a treatise on International Law were it not for the fact that many writers maintain that there are rules of International Law in existence which determine and define just causes of war. It must, however, be emphasised that this is by no means the case. All such rules laid down by writers on International Law as recognise certain causes as just and others as unjust are rules of writers, but not rules of International Law based on international custom or international treaties. [Sidenote: Causes of War.]