At 11:10 a.m. on July 28, 1914, Count Leopold von Berchtold, the Austro-Hungarian Minister for Foreign Affairs, sent a telegram to M.N. Pashitch, the Serbian Prime Minister and Minister for Foreign Affairs. The message read:
The Royal Serbian Government not having answered in a satisfactory manner the note of July 23, 1914, presented by the Austro-Hungarian Minister at Belgrade, the Imperial and Royal Government are themselves compelled to see to the safeguarding of their rights and interests, and, with this object, to have recourse to force of arms. Austria-Hungary consequently considers herself henceforward in state of war with Serbia.
Thus began World War I.
It was exactly one month after Archduke Franz Ferdinand of Austria and his wife were killed by a Serbian nationalist in Sarajevo. Emboldened by the support of its ally Germany, Austria-Hungary presented Serbia with an ultimatum demanding, among other things, that Austria-Hungary be allowed to conduct its own investigation into the archduke’s killing.
Serbia accepted all of Austria’s demands save one, yet the Austrian government broke diplomatic ties and began to prepare for war. At the same time, Serbia’s ally Russia began to mobilize its military against Austria.
Before the war was over, a total of 32 nations had joined forces against the Austria-Hungary/Germany/Turkey/Bulgaria alliance. One nation, Romania, actually entered the war twice. The first time was when it declared war with Austria-Hungary on Aug. 27, 1916. Those hostilities ended with the Treaty of Bucharest on May 7, 1918. But Romania again entered the war on Nov. 10, 1918, the day before the armistice was signed with the last combatant remaining from the Austria-Hungary/Germany/Turkey/Bulgaria alliance, Germany.