The Austrian annexation (1908) of Bosnia and Herzegovina created an international crisis, but war was avoided. The Balkan Wars (1912–13) remained localized but increased Austria's concern for its territorial integrity, while the solidification of the Triple Alliance made Germany more yielding to the demands of Austria, now its one close ally. The assassination (June 28, 1914) of Archduke Francis Ferdinand at Sarajevo set in motion the diplomatic maneuvers that ended in war.
The Austrian military party, headed by Count Berchtold, won over the government to a punitive policy toward Serbia. On July 23, Serbia was given a nearly unacceptable ultimatum. With Russian support assured by Sergei Sazonov, Serbia accepted some of the terms but hedged on others and rejected those infringing upon its sovereignty. Austria-Hungary, supported by Germany, rejected the British proposal of Sir Edward Grey (later Lord Grey of Fallodon) and declared war (July 28) on Serbia.
Russian mobilization precipitated a German ultimatum (July 31) that, when unanswered, was followed by a German declaration of war on Russia (Aug. 1). Convinced that France was about to attack its western frontier, Germany declared war (Aug. 3) on France and sent troops against France through Belgium and Luxembourg. Germany had hoped for British neutrality, but German violation of Belgian neutrality gave the British government the pretext and popular support necessary for entry into the war. In the following weeks Montenegro and Japan joined the Allies (Great Britain, France, Russia, Serbia, and Belgium) and the Ottoman Empire joined the Central Powers (Germany and Austria-Hungary). The war had become general. Whether it might have been avoided or localized and which persons and nations were most responsible for its outbreak are questions still debated by historians.
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