Why did Austria-Hungary occupy Bosnia-Herzegovina in 1878?

Austria-Hungary occupied Bosnia and Herzegovina in 1878 primarily to increase its influence in the Balkans and to reassert Habsburg interests in the region following the Russo-Turkish War of 1877–78.12

The occupation was sanctioned by the Congress of Berlin, a diplomatic meeting of major European powers held in 1878 to resolve international tensions caused by the Treaty of San Stefano. By allowing Austria-Hungary to occupy and administer the provinces—which remained nominally under the sovereignty of the Ottoman Empire—the Congress sought to counterbalance the growing influence of Russia in the region.13

For Franz Joseph, the occupation represented a significant foreign-policy success, which he had personally advocated for and which was executed by his foreign minister, Count Gyula Andrássy. While the occupation was initially intended to be temporary, the Habsburg administration invested heavily in the region's infrastructure and economy to integrate it more closely with the empire, eventually leading to the full annexation of the provinces in 1908.456