What was the spark that caused the powder keg of the balkans to explode and began world war 1?

The spark that ignited the powder keg of the Balkans and triggered World War I was the assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, in Sarajevo. The assassin, Gavrilo Princip, was a member of the nationalist group known as the Black Hand, which sought to promote Slavic nationalism and oppose Austro-Hungarian rule. This event set off a chain reaction of political tensions, alliances, and mobilizations, leading to the outbreak of war in July 1914 after Austria-Hungary issued an ultimatum to Serbia, which was partially rejected. Ultimately, this assassination highlighted the deep-rooted ethnic tensions and rivalries that existed in the region, which had been simmering for years.