Why did Austria-Hungary annex Bosnia and Herzegovina in 1908?

Austria-Hungary annexed Bosnia and Herzegovina in 1908 primarily to solidify its control over the region and prevent the newly established Young Turk government from reclaiming authority there.12

Following the Congress of Berlin in 1878, Austria-Hungary had been granted the right to occupy and administer the provinces, though they remained under the nominal sovereignty of the Ottoman Empire. By 1908, the Austrian foreign minister, Alois, Graf Lexa von Aehrenthal, feared that the constitutional reforms introduced by the Young Turks would undermine the Habsburg position in the territory.132

To secure the annexation, Aehrenthal reached a tentative agreement with the Russian foreign minister, Aleksandr P. Izvolsky, in which Russia would not object to the move in exchange for Austrian support for opening the Bosporus and Dardanelles straits to Russian warships. Although the annexation was finalized in October 1908, it triggered the Bosnian crisis of 1908, leading to severe international tension and lasting resentment from Serbia and Russia.12