Млада Босна
Austria-Hungary annexed Bosnia-Herzegovina on 6 October 1908, which caused the Annexation Crisis in Europe. The Kingdom of Serbia protested and mobilised its army, but then on 31 March 1909, it formally accepted the annexation. In 1911, Mladen Stojanović became a member of the secret association of students of the Tuzla gymnasium called "Narodno Jedinstvo" (National Unity); its members described it as a youth society of nationalists. It was one of a group of diverse student organisations later called Young Bosnia, which strongly opposed Austria-Hungary's rule over Bosnia-Herzegovina. The activists of Young Bosnia were Bosnian Serbs, Muslims, and Croats, though most were Serbs. The first organisation regarded to be part of this group was established in 1904 by Serb students of the Mostar gymnasium. 1905 saw considerable political unrest among the Serb and Croat students of the Tuzla gymnasium. Although the provincial government imposed the name "Bosnian" on the language of the province (Serbo-Croatian), the students demonstratively termed it as Serbian or Croatian depending on their ethnic affiliation.