By 1903 Balkan nationalism was asserting itself again. Serbia led the way, becoming openly hostile to both Austria-Hungary and the Ottoman Empire. The Slavic Serbs looked to Slavic Russia for support of their national aspirations. In 1908, to block Serbian expansion, Austria formally annexed Bosnia and Herzegovina. Serbia erupted in rage but could do nothing without Russia’s support.

Then two nationalist wars, the first and second Balkan wars in 1912 and 1913, finally destroyed the centuries-long Ottoman presence in Europe (Map 28.2). This sudden but long-expected event elated Balkan nationalists but dismayed Austria-Hungary’s leaders who feared that Austria-Hungary might next be broken apart.

Within this tense context, Serbian nationalist Gavrilo Princip assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, and his wife, Sophie, on June 28, 1914, during a state visit to the Bosnian capital of Sarajevo. Austria-Hungary’s leaders held Serbia responsible and on July 23 presented Serbia with an unconditional ultimatum that included demands amounting to Austrian control of the Serbian state. When Serbia replied moderately but evasively, Austria declared war.

Of prime importance in Austria-Hungary’s fateful decision was Germany’s unconditional support. Kaiser William II and his chancellor, Theobald von Bethmann-Hollweg, realized that war between Austria and Russia was likely, for Russia could not stand by and watch the Serbs be crushed. Yet Bethmann-Hollweg hoped that while Russia (and its ally France) might go to war, Great Britain would remain neutral.

Anticipating a possible conflict, Europe’s military leaders had been drawing up war plans and timetables for years, and now these, rather than diplomacy, began to dictate policy. Tsar Nicholas II ordered a partial mobilization against Austria-Hungary but almost immediately found this was impossible. Russia had assumed a war with both Austria and Germany, and it could not mobilize against one without mobilizing against the other. Therefore, Russia ordered full mobilization and in effect declared general war. The German general staff had also prepared for a two-front war. Its Schlieffen plan called for first knocking out France with a lightning attack through neutral Belgium to capture Paris before turning on a slower-to-mobilize Russia. On August 3 German armies invaded Belgium. Great Britain declared war on Germany the following day. In each country the great majority of the population rallied to defend its nation and enthusiastically embraced war in August 1914.