The Bosnian Crisis, also known as the Annexation Crisis (German: Bosnische Annexionskrise; Serbo-Croatian: Aneksiona kriza, ) or the First Balkan Crisis, erupted on 5 October 1908 when Austria-Hungary announced the annexation of Bosnia and Herzegovina, territories formerly within the sovereignty of the Ottoman Empire but under Austro-Hungarian administration since 1878.This unilateral actiontimed to coincide with Bulgaria's declaration of independence from the Ottoman Empire on 5 Octobersparked protestations from all the Great Powers and Austria-Hungary's Balkan neighbors, 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 and its neighbors, especially Serbia, Italy and Russia, and in the long term helped lay the grounds for World War I. Although the crisis ended with what appeared to be a total Austro-Hungarian diplomatic victory, the crisis destroyed any remaining ability for the Austrians and the Russians to cooperate in the Balkans and damaged Austrian relations with Serbia and the Italians. Austro-Serbian relations harmed by the annexation's inflaming of Serbian nationalists continued to be strained to the point of declaring war on each other in 1914.

Austria-Hungary, often referred to as the Austro-Hungarian Empire or the Dual Monarchy, was a constitutional monarchy and great power in Central Europe between 1867 and 1918. It was formed with the Austro-Hungarian Compromise of 1867 and was dissolved shortly after its defeat in the First World War.

At its core was the dual monarchy which was a real union between Cisleithania, the northern and western parts of the former Austrian Empire, and the Kingdom of Hungary. A third component of the union was the Kingdom of Croatia-Slavonia, an autonomous region under the Hungarian crown, which negotiated the Croatian–Hungarian Settlement in 1868. From 1878, Austria-Hungary jointly governed Bosnia-Herzegovina, which it annexed in 1908. Austria-Hungary was ruled by the House of Habsburg and constituted the last phase in the constitutional evolution of the Habsburg Monarchy. The union was established by the Austro-Hungarian Compromise on 30 March 1867 in the aftermath of the Austro-Prussian War. Following the 1867 reforms, the Austrian and Hungarian states were co-equal in power. The two states conducted common foreign, defense, and financial policies, but all other governmental faculties were divided among respective states.

Austria-Hungary was a multinational state and one of Europe's major powers at the time. Austria-Hungary was geographically the second-largest country in Europe after the Russian Empire, at 621,538 km2 (239,977 sq mi) and the third-most populous (after Russia and the German Empire). The Empire built up the fourth-largest machine building industry in the world, after the United States, Germany, and the United Kingdom. Austria-Hungary also became the world's third-largest manufacturer and exporter of electric home appliances, electric industrial appliances, and power generation apparatus for power plants, after the United States and the German Empire.After 1878, Bosnia and Herzegovina came under Austro-Hungarian military and civilian rule until it was fully annexed in 1908, provoking the Bosnian crisis among the other powers. The northern part of the Ottoman Sanjak of Novi Pazar was also under de facto joint occupation during that period, but the Austro-Hungarian army withdrew as part of their annexation of Bosnia. The annexation of Bosnia also led to Islam being recognized as an official state religion due to Bosnia's Muslim population .Austria-Hungary was one of the Central Powers in World War I, which began with an Austro-Hungarian war declaration on the Kingdom of Serbia on 28 July 1914. It was already effectively dissolved by the time the military authorities signed the armistice of Villa Giusti on 3 November 1918. The Kingdom of Hungary and the First Austrian Republic were treated as its successors de jure, whereas the independence of the West Slavs and South Slavs of the Empire as the First Czechoslovak Republic, the Second Polish Republic, and the Kingdom of Yugoslavia, respectively, and most of the territorial demands of the Kingdom of Romania were also recognized by the victorious powers in 1920.