On June 28, 1914, Archduke Franz Ferdinand of Austria, the heir to the Austro-Hungarian throne, and his wife Sophie, Duchess of Hohenberg, were assassinated in Sarajevo, the capital of Bosnia-Herzegovina (formally annexed by Austria-Hungary in 1908). The assassin, Gavrilo Princip, was a Bosnian Serb nationalist and member of the Black Hand, a secret society dedicated to the unification of all South Slavic peoples into a single state, free from Austro-Hungarian rule. The assassination sparked outrage and indignation throughout Europe and set in motion a chain of events that ultimately led to the outbreak of World War I.
Austria-Hungary's Ultimatum To Serbia
In the aftermath of the assassination, Austria-Hungary issued an ultimatum to Serbia, accusing the Serbian government of complicity in the plot and demanding that it take immediate steps to punish those responsible and prevent future subversive activities. The ultimatum was deliberately designed to be unacceptable, and when Serbia failed to comply fully with its terms, Austria-Hungary declared war on July 28, 1914.
Russian Mobilization
Russia, as Serbia's main ally and protector, viewed the Austrian declaration of war as a direct threat to its interests in the Balkans. In response, Russia ordered a general mobilization of its armed forces, which included moving troops towards the Austro-Hungarian border. This action alarmed Germany, which saw the Russian mobilization as a provocation and a threat to its own security.
Germany's Declaration Of War On Russia
On July 19, 1914, Germany issued an ultimatum to Russia, demanding the cessation of its military preparations within 12 hours. When Russia refused to comply, Germany declared war on Russia on August 1, 1914.
France Declares War On Germany
As Russia's ally, France was bound by the Franco-Russian Alliance of 1894 to support Russia in the event of war. Following Germany's declaration of war on Russia, France declared war on Germany on August 3, 1914.
Britain Declares War On Germany
Britain, traditionally a neutral power in continental European conflicts, was drawn into the war primarily due to the violation of Belgian neutrality by Germany. As a guarantor of Belgian independence, Britain issued an ultimatum to Germany demanding the withdrawal of German troops from Belgian territory. When Germany refused, Britain declared war on Germany on August 4, 1914, thus completing the formation of the two opposing alliances that would fight in World War I: the Allied Powers (primarily Britain, France, Russia, Italy, Japan, and the United States) and the Central Powers (Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria).