In 1878 Austria-Hungary gained some control over Bosnia-Herzegovinia, much to the disgust of Serbia. In 1903 the government in Serbia changed in a military uprising, and the government were favourable to conflict with Austria-Hungary over Bosnia. Many Serbs felt that Serbia and Bosnia should be a united country and by 1903 not only were the Serbian government willing to fight for this, but the terrorist Black Hand Gang were as well.
Relations between the two countries worsened in 1908 when Austria-Hungary formally "annexed" (took over) Bosnia as Turkey was losing control of his empire. Serbia were outraged, and along with their ally, Russia, they threatened war. Europe looked on the brink of war, with Germany willing to back Austria-Hungary. War was only avoided as Britain and France declared that they would not support Russia, despite their alliance. Russia were humiliated, and vowed not to back down the next time Serbia was threatened. Serbia reluctantly backed down, but the incident only increased tensions and the desire for a violent end to Austro-Hungarian rule in Bosnia.