Austro-Hungarian annexation of Bosnia and Herzegovina

The Bosnian crisis of 1908–09, also known as the Annexation crisis or the First Balkan Crisis, erupted when on 8 October 1908, Austria-Hungary announced the annexation of Bosnia and Herzegovina, territories formally within the sovereignty of the Ottoman Empire. This unilateral action—timed to coincide with Bulgaria's declaration of independence (5 October) from the Ottoman Empire—sparked protestations from all the Great Powers and Austria-Hungary's Balkan neighbours, Serbia and Montenegro. In April 1909 the Treaty of Berlin was amended to reflect the fait accompli and bring the crisis to an end. The crisis permanently damaged relations between Austria-Hungary on one hand and Serbia, Italy and the Russian Empire on the other. The Italian historian Luigi Albertini regarded it as laying the grounds for World War I. Although the crisis ended with what appeared to be a total Austro-Hungarian diplomatic victory, Russia became determined not to back down again and hastened its military build-up. Austrian–Serbian relations became permanently stressed.

The mid-1870s witnessed a series of violent rebellions against Ottoman rule in the Balkans, and equally violent and repressive responses from the Turks. The Russian Tsar, Alexander II, wanting to intervene against the Ottomans, sought and obtained an agreement with Austria-Hungary. In the Budapest Conventions of 1877, the two powers agreed that Russia would annex Bessarabia, and Austria-Hungary would observe a benevolent neutrality toward Russia in the pending war with the Turks. As compensation for this support, Russia agreed to Austria-Hungary's annexation of Bosnia-Herzegovina.

Shortly thereafter, the Russians declared war, and, after a few setbacks, drove the Turks relentlessly back to within a few miles of Istanbul. What stopped the Russians from driving the Turks completely out of Europe was the willingness of the other great powers, particularly Britain and Austria-Hungary, to enforce an earlier treaty, the London Straits Convention of 1841, which stated that the Straits of Constantinople would be closed to warships during time of war. This had the effect of bottling up the Russian fleet in the Black Sea, but would be worthless if Russian troops gained control of the straits by land.

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