On July 28th, Austria-Hungary declared war on Serbia, after declaring themselves unsatisfied with Serbia's not-quite-complete capitulation to an ultimatum Austria-Hungary had sent on the 23rd. Austro-Hungarian gunboats on the Danube shelled Belgrade to show that the declaration was serious, but then for several days very little happened. Austria-Hungary and Serbia had both mobilized, but the Hapsburg military was so ponderous in its mobilization that it was a week until the first battle between Serbia and Austria-Hungary.
Russia had begun mobilizing its armies in response to the Austro-Hungarian declaration of war, but did not cross the border. On July 31st Germany demanded that Russia stop mobilizing, and when Russia failed to do so, Germany declared war on Russia on August 1st.
On August 2nd Germany invaded Luxembourg in order to use it as a staging ground for its invasion of France. On that same day, a single German cavalry patrol crossed into France and exchanged fire with four French border guards, resulting in the first deaths on the Western Front.
On August 3rd Germany declared war on France, and Belgium refused a German demand to allow its armies to pass through on the way to invade France.
Finally, on August 4th Germany invaded Belgium and Great Britain, as a result, declared war on Germany.
The war thus took a full week to fully start. Up until Germany attacked France and Belgium, there was still a possibility of the war remaining a regional conflict between Austria-Hungary and Serbia, though Russia's mobilization suggests that it might have intervened eventually even in such a local conflict.
|French heavy cavalry mobilize in 1914.|