July 28 - Austria-Hungary declares war

Franz Conrad von Hotzendorf

At 11am Austria-Hungary declared war on Serbia, confident of Germany's support.

Remarkably this could not lead to an immediate full-scale invasion. On 26 July Franz Conrad von Hotzendorf, Chief of the General Staff, had told Count Berchtold that this would be impossible for a number of weeks.

Even more remarkably, earlier that morning, the Kaiser had read for the first time the full text of the Austro-Hungarian ultimatum and the Serbian response. The Kaiser could see no reason for any declaration of war, commenting, "A great moral victory for Vienna; but with it every reason for war is removed."

This untimely incident remained secret until after the war. 

The Kaiser

Unfortunately it was too late, since Austria-Hungary's
declaration of war took place an hour or so later.

July 5 - The start of the "July Crisis"

Bethmann-Hollweg, German Chancellor

In early July, following the assassination of the Archduke, the Austro-Hungarians sent Count Hyos, Count Berchtold's principal aide at the Foreign Ministry, to find out what the Germans would do after Sarajevo. Count Hyos discussed this with the Austro-Hungarian Ambassador in Berlin, Count Szogyeny. On 5 July, Count Szogyeny was given a special audience with Kaiser Wilhelm II in the New Palace at Potsdam.

During the course of this audience, the Kaiser gave the assurances sought: that Austro-Hungary could count on Germany's support if Russia were to intervene in support of Serbia. That evening Szogeyeny cabled Count Berchtold that he had received "full German backing" in any action that Vienna decided to take, even if "serious European complications" resulted, requesting only that it would be done speedily.

The Kaiser's pledge was confirmed the following day by the German Chancellor, Bethmann-Hollweg and Arthur Zimmermann, the Under Secretary of State. The "July Crisis" had started.