One hundred years ago today, July 23, 1914, at 6:00 PM Belgrade time, the Austria-Hungarian ambassador to Serbia presented a note (somewhat speciously not an ultimatum) to the Serbian government: Serbia had 48 hours to meet the 10 demands presented by Austria-Hungary or face war.
Six of the ten were essentially public relation issues, but four demanded Austria-Hungarian participation and oversight of the Serbian investigation into the murder of Archduke Franz Ferdinand, a clear intrusion into Serbia’s sovereignty. Serb nationalism had long been Austria-Hungary’s thorniest problem, and the note was a prelude to a punitive war with Serbia long desired by Austria-Hungary.
Because Russia, a great power in her own right, was protective of Serbia, Austria-Hungary did not dare act on its own. Prior to drafting and delivering the note/ultimatum to Serbia, Austria-Hungary had sought and obtained Germany’s backing (Kaiser Wilhelm II himself assured the Austrians that such backing would be forthcoming). The Kaiser discounted the possibility that Russia would intervene in Serbia’s defense, as did his closest advisors.
If the Kaiser was wrong (and of course we now know he was), Russia would intervene against Austria-Hungary in Serbia’s defense, causing Germany to have to intervene (by treaty) against Russia. Because France was bound by treaty to defend Russia, a German attack against Russia would mean war with France as well.
Thus, if the Kaiser got it wrong, that meant an almost inevitable general war in Europe, with Germany and Austria-Hungary facing off against France and Russia. Britain was not bound by treaty (contrary to popular belief) to defend either France or Russia, but the British did have an understanding with France that either country would support the other if common vital interests were threatened. If not actively a belligerent, Britain would certainly commit her enormous economic resources for France and Russia and against Germany.
The initial reaction of the Serbs to the Austrian note/ultimatum was fear and a willingness to compromise. Her tiny army was no match for Austria-Hungary, and there was no guarantee Russia would come to Serbia’s aid (Russia had not acted to halt Bulgaria’s defeat in the Second Balkan War in 1913).
Thus, by the end of July 14, 1914, a day after receiving the note/ultimatum and with a day to go before its expiration, Serbia appeared ready to cave in. Had it done so, no war would have ensued.
Then Russia intervened.
Source: John Keegan, The First World War.
Czar Nicholas II