Gavrilo Princip, the man remembered in history as the man who shot and killed the Austro-Hungarian prince Franz Ferdinand, died on this day (28 April) in 1918 in a Czech prison in Terezin fortress.
In 1908, the Austro-Hungarian Monarchy announced the annexation of Bosnia and Herzegovina, which meant the complete annexation of its territory into Austria-Hungary as a sovereign state, which caused strong reactions in Serbia and Bosnia.
The crisis ended on March 31st, 1909, when Serbia and Russia, under the threat of war, were forced to sign a statement that they don’t have anything against the annexation.
Franz Ferdinand arrived in Sarajevo on 28 June 1914, to lead the military maneuvers that were performed near the city. The Serbian population saw this as a provocation, since the event took place on Vidovdan, a historically important day for the Serbs. Therefore, this is considered to be one of the reasons for the assassination.
The Austro-Hungarian authorities came to the conclusion during the investigation that the weapon used in the assassination came from Serbia. Although this incident was not related to official authorities of the Kingdom of Serbia, the Austro-Hungarian authorities took advantage of the situation to send an ultimatum to Serbia, knowing that Serbia could never accept it.
The Serbian authorities responded positively to all points of the ultimatum but one that meant occupation of the territory of the Kingdom of Serbia. The British cabinet, just after receiving the news of the Austrian ultimatum to Serbia, held a meeting in London and concluded that such ultimatum had never been penned in modern times and that it seemed absolutely impossible that any state in the world could accept it, or that any acceptance, however abject, would satisfy the aggressor. The Austro-Hungarian authorities used this situation to declare war to Serbia, which quickly escalated into the First World War.
Source: fb page Meet the Serbs