Austro-Hungarian occupation of Serbia

The Austro-Hungarian Armed Forces occupied Serbia from late 1915 until the end of World War I. Austria-Hungary's declaration of war against Serbia on 28 July 1914 marked the beginning of the war. After three unsuccessful Austro-Hungarian offensives between August and December 1914, a combined Austro-Hungarian and German offensive breached the Serbian front from the north and west in October 1915, while Bulgaria attacked from the east.

Source: Wikipedia — Austro-Hungarian occupation of Serbia (CC BY-SA 4.0)