July Crisis - Wikipedia

On July 28, 1914, Austria-Hungary decided against mediation and declared war on Serbia, the first declaration of war of WWI. From the article:

"At 11:00 a.m. on 28 July, Austria declared war on Serbia.[124] Following instructions from Bethmann Hollweg, von Tschirschky did not present Wilhelm’s "Stop in Belgrade" proposal until noon.[124] At 1:00am on 29 July 1914 the first shots of the First World War were fired by the Austrian monitor SMS Bodrog, which bombarded Belgrade in response to Serbian sappers blowing up the railway bridge over the river Sava which linked the two countries.[147] In Russia, partial mobilization was ordered for the four military districts bordering Austria-Hungary.[148] Wilhelm sent a telegram to Nicholas asking for Russian support for the Austrian war against Serbia.[148] Nicholas replied: "Am glad you are back ... I appeal to you to help me. An ignoble war has been declared on a weak country ... Soon I shall be overwhelmed by pressure brought upon me ... to take extreme measures which will lead to war. To try and avoid such as a calamity as a European war, I beg you in the name of our old friendship to do what you can to stop your allies from going too far."[136]

Shortly after declaring war on Serbia, Conrad informed the Germans that Austria-Hungary could not start operations until 12 August, to much fury in Berlin.[124] Bavarian diplomat Count Lerchenfeld reported to Munich: "The Imperial government is thus put into the extraordinary difficult position of being exposed during the intervening period to the other Powers’ proposals for mediation and conferences, and if it continues to maintain its previous reserve towards such proposals, the odium of having provoked a world war will in the end recoil on it, even in the eyes of the German people. But a successful war on three fronts (viz, in Serbia, Russia and France) can not be initiated and carried on such a basis. It is imperative that the responsibility for any extension of the conflict to the Powers not directly concerned should under all circumstances fall on Russia alone."[149] At the same time, the German Ambassador to Russia, Portalés, reported that, based on a conversation with Sazonov, Russia was prepared to make "astonishing" concessions by promising to pressure Serbia to agree to most of the Austrian demands to avoid a war. The prospect of talks was rejected out of hand by Bethmann Hollweg.[150]

Through as late as 27 July, Jagow expressed the view that Russian partial mobilization against the frontiers of Austria-Hungary was not a casus belli, Moltke instead argued that Germany should mobilize at once and attack France. Moltke was overruled by Bethmann Hollweg in two meetings on 29 July, who argued that Germany should wait for Russia to begin a general mobilization. As Bethmann Hollweg told Moltke, this was the best way to ensure that blame for the "whole shemozzle" could be placed on Russia’s door, and thus ensure British neutrality.[150] While promising not to start mobilization without the Chancellor's orders, Moltke ordered the German military attaché in Belgium to ask for permission for German troops to cross through on the way to attack France.[151] Also on July 28, Bethmann Hollweg offered to form an anti-Russian military alliance with Turkey."