Summary/Abstract: The campaigns of the Austro-Hungarian army against Serbia in 1914 and in combination with the German Empire and Bulgaria in fall 1915 distinguish in their strategic perspective but are quite similar concerning the special characteristics of the fighting going on. Both operations were deeply influenced by tactics of mountain warfare. In 1914 the k. u.k. Headquarter of the Balkan-Forces had to deal with the strategic problem of defending the border to Bosnia-Herzegovina on the one hand and defeating the Serbian Army on the other hand, having not enough forces to fulfill both missions. In addition to that, the Serbian Army – fully experienced in modern mountain warfare and equipped with modern artillery – was fighting on own territory performing high effective in defending their ground and fighting the small war. In combination with already outdated war plans and mistakes in the initial concentrating of all forces, all three offensives led to a total disaster causing enormous casualties for the k. u.k. forces. Because of the agreement of executing a multinational and combined operation on Serbia in 1915, the German Empire and the Kingdom of Bulgaria together with the Austro-Hungarian Army managed to deploy enough forces to defeat the Serbian Army. The allied forces again faced the problems of modern mountain warfare especially slow advancements caused by the lack of streets and communication lines making rapid operations almost impossible. The outnumbered Serbian Army had to face heavy casualties but managed to avoid full annihilation and reached the Adriatic coast for evacuation.
