Hostilities between Austria-Hungary and Serbia had been escalating following the June 28 assassination in Sarajevo of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne.
Anticipating Russian militarism, Austria-Hungary sought German support for a war against Serbia.
Germany agreed to support Austria-Hungary, and on July 28 Austria-Hungary declared war on Serbia.
Russia subsequently mobilised.
Events of August 1:
- Germany declares war on Russia
- Italy declares its neutrality
- Germany and the Ottoman Empire sign a secret alliance treaty. The alliance was created as part of a joint-cooperative effort intended to strengthen and modernize the ailing Ottoman military, as well as provide Germany safe passage into neighbouring British colonies.