HISTORICAL BACKGROUND
On 28 June 1914, Archduke Franz Ferdinand of Austria and his wife were shot dead in Sarajevo, by Gavrilo Princip, member of the Black Hand, a political organization seeking for a merging of the Balkan area into a Greater Serbia or a Yugoslavia.
Austria-Hungary subsequently issued an ultimatum against Serbia. As the ultimatum was rejected, Austria-Hungary then declared war, marking the outbreak of the war.
While France and Russia immediately sided with Serbia, Germany joined the Austria-Hungary and started a surprise offensive in the west with the objective of quickly defeating the French, to then turn east and knock the Tzarist Russia out of the war.