In 1903, the king of Serbia was murdered and replaced with Peter I. After this, Serbia became more nationalist. Tensions with Austria-Hungary heightened when it conquered Bosnia in 1908. During this period Serbia managed to extend its borders and reconquer Kosovo and North Macedonia from the Ottoman Empire. Many Serbian nationalists wanted to create a unified state for the Slavs of the Balkans. Covert gangs attempted to assassinate Austro-Hungarian officials, like the Bosnian governor. In June 1914, a Bosnian Serb called Gavrilo Princip killed Austrian Archduke Franz Ferdinand in Sarajevo, Bosnia. This event eventually led to World War I.