Final answer:
A member of the Slavic resistance group known as the Black Hand assassinated Archduke Franz Ferdinand of Austria-Hungary in Sarajevo on June 28, 1914, sparking the start of World War I.
Step-by-step explanation:
Prior to the outbreak of World War 1, a member of a Slavic resistance group assassinated the heir to the throne of Austria-Hungary in Sarajevo. The Archduke Franz Ferdinand and his wife, Sophia, were killed by Gavrilo Princip, a member of the Serbian nationalist group known as the Black Hand.
This assassination took place on June 28, 1914, during an official visit to the regional capital of Sarajevo. The goal of this act was to promote Slavic nationalism and to contribute to the separation of Bosnia-Herzegovina from the Austro-Hungarian Empire.
The complex web of alliances in Europe led this incident to trigger the start of World War I, with Austria-Hungary's declaration of war on Serbia invoking several countries into the conflict based on alliance systems.