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.