Bosnia and Herzegovina fell under Austro-Hungarian rule in 1878 when the Congress of Berlin approved the occupation of the Bosnia Vilayet, which officially remained part of the Ottoman Empire. Three decades later, in 1908, Austria-Hungary provoked the Bosnian crisis by formally annexing the occupied zone, establishing the Condominium of Bosnia and Herzegovina under the joint control of Austria and Hungary.

Following the Russo-Turkish War of 1877-78, in June and July 1878 the Congress of Berlin was organized by the Great Powers. The resulting Treaty of Berlin caused Bosnia and Herzegovina to nominally remain under sovereignty of the Ottoman Empire, but was de facto ceded to Austria-Hungary, which also obtained the right to garrison the Sanjak of Novi Pazar. According to article 25:

The provinces of Bosnia and Herzegovina shall be occupied and administered by Austria-Hungary. The government of Austria-Hungary, not desiring to undertake the administration of the Sanjak of Novi-Pazar, which extends between Serbia and Montenegro in a South-Easterly direction to the other side of Mitrovitza, the Ottoman administration will continue to exercise its functions there. Nevertheless, in order to assure the maintenance of the new political state of affairs, as well as freedom and security of communications, Austria-Hungary reserves the right of keeping garrisons and having military and commercial roads in the whole of this part of the ancient vilayet of Bosnia. To this end the governments of Austria-Hungary and Turkey reserve to themselves to come to an understanding on the details.

The Austro-Hungarian Army engaged in a major mobilization effort to prepare for the assault on Bosnia and Herzegovina, commanding by the end of June 1878 a force of 82,113 troops, 13,313 horses and 112 cannons in the VI, VII, XX, and XVIII infantry divisions as well as a rear army in the Kingdom of Dalmatia. The primary commander was Josip Filipović; the forward XVIII infantry division was under the command Stjepan Jovanović, while the rear army commander in Dalmatia was Gavrilo Rodić. The occupation of Bosnia and Herzegovina started on 29 July 1878 and was over on 20 October.

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Wikipedia