Complex sentence: Serbia's victories in the Austro-Hungarian invasion in 1914 in the of 1908--1909 by unlawful annexing the former Ottoman territory of Bosnia and Herzegovina, which it had occupied since 1878.
Split into simpler sentences: Serbia's victories in the Austro-Hungarian invasion in 1914. Austria-Hungary precipitated the Bosnian crisis of 1908--1909 by unlawful annexing the former Ottoman territory of Bosnia and Herzegovina, which it had occupied since 1878.