§ 93. According to the former practice of the States a condition of war could _de facto_ arise either through a declaration of war; or through a proclamation and manifesto of a State that it considered itself at war with another State; or through the committal by one State of certain hostile acts of force against another State. History presents many instances of wars commenced in one of these three ways. Although Grotius (III. c. 3, § 5) laid down the rule that a declaration of war is necessary for its commencement, the practice of the States shows that this rule was not accepted, and many wars have taken place between the time of Grotius and our own without a previous[172] declaration of war. Indeed many writers,[173] following the example of Grotius, have always asserted the existence of a rule that a declaration is necessary for the commencement of war, but it cannot be denied that until the Second Peace Conference of 1907 such a rule was neither sanctioned by custom nor by a general treaty of the Powers. Moreover many writers[174] distinctly approved of the practice of the Powers. This does not mean that in former times a State would have been justified in opening hostilities without any preceding conflict. There was, and can be, no greater violation of the Law of Nations than for a State to begin hostilities in time of peace without previous controversy and without having endeavoured to settle the conflict by negotiation.[175] But if negotiation had been tried without success, a State did not act treacherously in case it resorted to hostilities without a declaration of war, especially after diplomatic intercourse had been broken off. The rule, adopted by the First Peace Conference of 1899--see article 2 of the Conventions for the peaceful settlement of international differences of 1899 and 1907--which stipulates that, _as far as circumstances allow_, before the appeal to arms recourse must be had to the good offices or mediation of friendly Powers, did not essentially alter matters, for the formula _as far as circumstances_ _allow_ leaves practically everything to the discretion of the Power bent on making war.